Adherence to antiretrovirals by pregnant women (and postpartum women if breastfeeding) is crucial to effectively decrease maternal viral load and decrease the risk of mother-to-child transmission of HIV. Our objectives were to describe self-reported adherence to antiretrovirals during the antepartum (after 22 weeks of pregnancy) and postpartum periods (6–12 weeks and 6 months), and identify predictors of adherence among HIV-infected women enrolled and followed in a prospective cohort study from June 2008 to June 2010 at multiple sites in Latin America. Adherence was evaluated using the number of missed and expected doses during the 3 days before the study visit. At the pre-delivery visit, 340 of 376 women (90%) reported perfect adherence. This rate significantly decreased by 6–12 weeks (171/214 [80%]) and 6 months postpartum (163/199 [82%], p<0.01). The odds for less than perfect adherence at the pre-delivery visit was significantly higher for pregnant women with current tobacco use (odds ratio [OR]=2.9, 95% confidence interval [CI]: 1.46–6.14; p=0.0029). At 6–12 weeks postpartum, the probability of non-perfect adherence increased by 6% for each 1 year increase in age (OR=1.06, 95% CI: 1.00–1.12, p=0.0497). At 6 months postpartum, the odds of nonperfect adherence was higher for those who were currently using alcohol (OR=3.04, 95% CI: 1.34–6.90; p=0.0079). Although a self-report measure of adherence based on only 3 days may lead to overestimation of actual adherence over time, women with perfect adherence had lower viral loads and higher CD4 counts. Adherence to antiretrovirals decreased significantly postpartum. Interventions should target women at high risk for lower adherence during pregnancy and postpartum, including tobacco and alcohol users.
We report evidence of low bone mass in behaviorally human immunodeficiency virus (HIV)–infected young men on antiretroviral therapy with a relatively recent diagnosis of HIV infection, compared with seronegative controls.
Background. Peak bone mass is achieved in adolescence/early adulthood and is the key determinant of bone mass in adulthood. We evaluated the association of bone mass with human immunodeficiency virus (HIV) infection and antiretroviral therapy (ART) during this critical period among behaviorally HIV–infected young men and seronegative controls.
Methods. HIV-positive men (N = 199) and HIV-negative controls (N = 53), ages 14–25 years, were studied at 15 Adolescent Trials Network for HIV/AIDS Interventions sites. HIV-positive participants were recruited on the basis of ART status: ART-naive (N = 105) or on a regimen containing a nonnucleoside reverse transcriptase inhibitor (NNRTI; N = 52) or protease inhibitor (PI; N = 42). Bone mineral density (BMD) and content (BMC) and body composition were measured by dual-energy X-ray absorptiometry (DXA). Results were compared across groups by linear modeling. Bone results were adjusted for race, body mass index (BMI), and type of DXA (Hologic/Lunar).
Results. The HIV-positive and HIV-negative groups had comparable median age (21 years) and racial/ethnic distribution. Median times since HIV diagnosis were 1.3, 1.9, and 2.2 years in the ART-naive, NNRTI, and PI groups, respectively (P = .01). Total and regional fat were significantly lower in the ART-naive group compared with seronegative controls. Mean BMD and Z scores were generally lower among HIV-positive participants on ART, particularly in the PI group. Average Z scores for the spine were below zero in all 4 groups, including controls.
Conclusions. Young men on ART with a relatively recent diagnosis of HIV infection have lower bone mass than controls. Longitudinal studies are required to determine the impact of impaired accrual or actual loss of bone during adolescence on subsequent fracture risk.
Pleistocene climatic oscillations have played a major role in structuring present-day biodiversity. The southern Mediterranean peninsulas have long been recognized as major glacial refugia, from where Northern Europe was post-glacially colonized. However, recent studies have unravelled numerous additional refugia also in northern regions. We investigated the phylogeographic pattern of the widespread Western Palaearctic lizard Podarcis muralis, using a range-wide multilocus approach, to evaluate whether it is concordant with a recent expansion from southern glacial refugia or alternatively from a combination of Mediterranean and northern refugia.
We analyzed DNA sequences of two mitochondrial (cytb and nd4) and three nuclear (acm4, mc1r, and pdc) gene fragments in individuals from 52 localities across the species range, using phylogenetic and phylogeographic methods. The complex phylogeographic pattern observed, with 23 reciprocally monophyletic allo- parapatric lineages having a Pleistocene divergence, suggests a scenario of long-term isolation in multiple ice-age refugia across the species distribution range. Multiple lineages were identified within the three Mediterranean peninsulas – Iberia, Italy and the Balkans - where the highest genetic diversity was observed. Such an unprecedented phylogeographic pattern - here called “refugia within all refugia” – compasses the classical scenario of multiple southern refugia. However, unlike the southern refugia model, various distinct lineages were also found in northern regions, suggesting that additional refugia in France, Northern Italy, Eastern Alps and Central Balkans allowed the long-term persistence of this species throughout Pleistocene glaciations.
The phylogeography of Podarcis muralis provides a paradigm of temperate species survival in Mediterranean and extra-Mediterranean glacial refugia. Such refugia acted as independent biogeographic compartments for the long-term persistence of this species, for the differentiation of its genetic lineages, and for the short-distance post-glacial re-colonization of neighbouring areas. This finding echoes previous findings from recent phylogeographic studies on species from temperate ecoregions, thus suggesting the need for a reappraisal of the role of northern refugia for glacial persistence and post-glacial assembly of Holarctic biota.
Podarcis muralis; Phylogeography; Western Palaearctic; Glacial refugia; Mediterranean peninsulas; Genetic diversity; Temperate species
This study evaluated a wide range of viral load (VL) thresholds to identify a cut-point that best predicts new clinical events in children on stable highly-active antiretroviral therapy (HAART).
Cox proportional hazards modeling was used to assess the adjusted risk of World Health Organization stage 3 or 4 clinical events (WHO events) as a function of time-varying CD4, VL, and hemoglobin values in a cohort study of Latin American children on HAART ≥ 6 months. Models were fit using different VL cut-points between 400 and 50,000 copies/mL, with model fit evaluated on the basis of the minimum Akaike Information Criterion (AIC) value, a standard model fit statistic.
Models were based on 67 subjects with WHO events out of 550 subjects on study. The VL cutpoints of > 2600 copies/mL and > 32,000 copies/mL corresponded to the lowest AIC values and were associated with the highest hazard ratios [2.0 (p = 0.015) and 2.1 (p = 0.0058), respectively] for WHO events.
In HIV-infected Latin American children on stable HAART, two distinct VL thresholds (> 2,600 copies/mL and > 32,000 copies/mL) were identified for predicting children at significantly increased risk of HIV-related clinical illness, after accounting for CD4 level, hemoglobin level, and other significant factors.
Pediatric HIV infection; viral load monitoring; viral load threshold; Latin America
No standardized guidelines exist for the biostatistical methods appropriate for studies evaluating diagnostic tests. Publication recommendations such as the STARD statement provide guidance for the analysis of data, but biostatistical advice is minimal and application is inconsistent. This article aims to provide a self-contained, accessible resource on the biostatistical aspects of study design and reporting for investigators. For all dichotomous diagnostic tests, estimates of sensitivity and specificity should be reported with confidence intervals. Power calculations are strongly recommended to ensure that investigators achieve desired levels of precision. In the absence of a gold standard reference test, the composite reference standard method is recommended for improving estimates of the sensitivity and specificity of the test under evaluation.
The objective of this study was to evaluate the performance of CHROMagar Acinetobacter when compared to sheep blood agar, MacConkey agar and MacConkey agar with 6 µg/ml of imipenem for the detection of A. baumannii in surveillance cultures of hospitalized patients. We utilized peri-anal swabs and sputum samples from patients admitted to the University of Maryland Medical Center ICUs from December 7 through December 21, 2009. Samples were plated onto four media in the following order: (1) 5% sheep blood agar (SBA), (2) MacConkey agar, (3) MacConkey agar with 6 µg/ml of imipenem, and (4) CHROMagar Acinetobacter (CHROMagar). SBA was the gold standard to which all media was compared. There were 165 samples collected during the study period. SBA and CHROMagar detected 18 of 18 (100%) Acinetobacter and 11 of 11 (100%) MDR-A. baumannii. MacConkey agar detected 16 of 18 (89%) Acinetobacter and 10 of 11 (91%) MDR- A. baumannii while MacConkey agar with 6 µg/ml imipenem detected 9 of 11 (82%) MDR-A. baumannii. CHROMagar did not differentiate MDR- A. baumannii from non-MDR-A. baumannii. CHROMagar may be useful for rapid detection of patients with MDR-A. baumannii if improved upon to better select for MDR-A. baumannii.
PM00104 binds guanines at DNA minor grooves, impacting DNA replication and transcription. A phase I study was undertaken to investigate safety, dose-limiting toxicities (DLTs), recommended phase II dose (RP2D), pharmacokinetics (PKs) and preliminary antitumour activity of PM00104 as a 1- or 3-h infusion three-weekly.
Patients with advanced solid tumours received PM00104 in a dose escalation trial, as guided by toxicity and PK data.
A total of 47 patients were treated; 27 patients on the 1-h schedule (0.23–3.6 mg m−2) and 20 patients on the 3-h schedule (1.8–3.5 mg m−2). Dose-limiting toxicities comprised reversible nausea, vomiting, fatigue, elevated transaminases and thrombocytopenia, establishing the 1-h schedule RP2D at 3.0 mg m−2. With the 3-h schedule, DLTs of reversible hypotension and neutropenia established the RP2D at 2.8 mg m−2. Common PM00104-related adverse events at the RP2D comprised grade 1–2 nausea, fatigue and myelosuppression. In both schedules, PKs increased linearly, but doses over the 1-h schedule RP2D resulted in higher than proportional increases in exposure. A patient with advanced urothelial carcinoma had RECIST shrinkage by 49%, and three patients had RECIST stable disease ⩾6 months.
PM00104 is well tolerated, with preliminary evidence of antitumour activity observed. The 1-h 3-weekly schedule is being assessed in phase II clinical trials.
cytotoxic; novel marine-derived compound; phase I; PM00104
A 71-year-old female presented with recurrent sigmoid volvulus. In the current admission, her symptoms were not settling on conservative measures and subsequently went on to have laparotomy. During laparotomy, along with the sigmoid volvulus, there was associated gallbladder torsion. About 500 cases of gallbladder volvulus have been published in literature, however, in our literature search, the authors did not find any similar published case presenting with volvulus involving the gallbladder and the sigmoid colon at the same time. This patient went onto have cholecystectomy and sigmoid colectomy and had a good postoperative recovery and was discharged on the tenth postoperative day.
At 6-week postoperative follow-up, she was doing well with no specific concerns.
Autotransporters are secreted proteins produced by pathogenic Gram-negative bacteria. They consist of a membrane embedded β-domain and an extracellular passenger domain that is sometimes cleaved and released from the cell surface. We solved the structures of three non-cleavable mutants of the autotransporter EspP to examine how it promotes asparagine cyclization to cleave its passenger. We found that cyclization is facilitated by multiple factors. The active site asparagine is sterically constrained to conformations favorable for cyclization while electrostatic interactions correctly orient the carboxamide group for nucleophilic attack. During molecular dynamics simulations, water molecules were observed to enter the active site and form hydrogen bonds favorable for increasing the nucleophilicity of the active site asparagine. When the activated asparagine attacks its main chain carbonyl carbon the resulting oxyanion is stabilized by a protonated glutamate. Upon cleavage, this proton could be transferred to the leaving amine group helping overcome a significant energy barrier. Together these findings provide insight into factors important for asparagine cyclization, a broadly used mechanism for protein cleavage.
EspP; autocleavage; outer membrane protein; crystal structure; asparagine cyclization
Lying in a shallow continental shelf cyclically affected by oscillating sea levels since the Miocene, the Seychelles islands are particularly interesting for evolutionary studies. Recent molecular studies are generating an emerging picture of the origin of its biota, yet very little is known regarding their phylogeographic structure or on the factors promoting diversification within the archipelago. Here we aimed to obtain a detailed depiction of the genetic structure and evolution of one of the most widespread vertebrate groups in the archipelago: the day-geckos of the genus Phelsuma. In parallel, we aimed to infer divergence times between species and subspecies, testing a long-standing hypothesis that argues for different time since sympatry between species as the cause of their different morphological differentiation across the archipelago.
Molecular data corroborated the existence of two main lineages, corresponding to the two currently recognized species. Divergences between species likely date back to the Mio-Pliocene, while more recent, Pleistocenic, divergences are suggested within each species. Populations from outer islands share mtDNA haplotypes with inner island populations, suggesting very recent dispersals (or introductions). We found no evidence of current gene flow between species, but results pointed to the possibility of gene flow between (now allopatric) subspecies. Time estimates suggest a synchronous divergence within each species (between island groups).
The geographic patterns of genetic variation agree with previous taxonomic subdivisions within each species and the origin of outer islands populations is clearly tracked. The similar intraspecific divergence time estimates obtained suggest that the differential body-size differentiation between species within each group of islands may be driven by factors other than character displacement proportional to time since sympatry, as previously suggested. These factors could include different habitats/resources available within each island group, niche differentiation and/or character displacement. We also bring again into consideration the hypothesis of body size being influenced by the distribution of native vegetation and social systems within this group, although it remains to be tested. Our results highlight not only the necessity of clarifying the role of ecology and interspecific interactions in this group’s morphological diversification and community assemblage, but also the importance of co-evolutionary mechanisms and their importance for appropriate conservation of island biodiversity. Further, we provide a detailed description of the phylogeographic structure of these taxa across these islands, which still remain poorly characterized in this respect.
Phelsuma; Seychelles; Phylogeography; Species-trees; Diversification; Morphological evolution; Character displacement; Biogeography
Contact precautions, used to reduce the transmission of infectious diseases, include the wearing of gowns and gloves for room entry. Previous small studies have shown an association between contact precautions and increased symptoms of depression and anxiety. A retrospective cohort of all patients admitted to a tertiary care centre over two years was studied to assess the relationship between contact precautions and depression or anxiety. During the two-year period, there were 70 275 admissions including 28 564 unique non-intensive-care-unit (ICU), non-psychiatric admissions. After adjusting for potential confounders, contact precautions were associated with depression [odds ratio (OR) 1.4, 95% confidence interval (CI) 1.2–1.5] but not with anxiety (OR 0.8, 95% CI 0.7–1.1) in the non-ICU population. Depression was 40% more prevalent among general inpatients on contact precautions.
Atlantolacerta andreanskyi is an enigmatic lacertid lizard that, according to the most recent molecular analyses, belongs to the tribe Eremiadini, family Lacertidae. It is a mountain specialist, restricted to areas above 2400 m of the High Atlas Mountains of Morocco with apparently no connection between the different populations. In order to investigate its phylogeography, 92 specimens of A. andreanskyi were analyzed from eight different populations across the distribution range of the species for up to 1108 base pairs of mitochondrial DNA (12S, ND4 and flanking tRNA-His) and 2585 base pairs of nuclear DNA including five loci (PDC, ACM4, C-MOS, RAG1, MC1R).
The results obtained with both concatenated and coalescent approaches and clustering methods, clearly show that all the populations analyzed present a very high level of genetic differentiation for the mitochondrial markers used and are also generally differentiated at the nuclear level.
These results indicate that A. andreanskyi is an additional example of a montane species complex.
Atlantolacerta andreanskyi; Lacertidae; Mountain specialist; High Atlas Mountains; Phylogeography; Morocco
Adolescents and young adults comprise disproportionately high percentages of individuals living with HIV and those with undiagnosed HIV. Our objective was to determine factors associated with history of HIV testing and receipt of results among a sample of urban, high-risk, sexually active adolescents in 15 U.S. cities.
20–30 sexually active youth, aged 12–24 years, were recruited to participate in an anonymous survey and HIV antibody testing at 2–3 venues per city identified by young men who have sex with men, young women of color, or intravenous drug users.
Of the 1457 participants, 72% reported having been previously tested for HIV (89% of whom were aware of their test results). Our sample was diverse in terms of gender, race/ethnicity, and sexual orientation. Factors found to be predictive of testing typically reflect high risk for HIV, except for some high risk partner characteristics, including having had a partner that made the youth have sex without a condom or had a partner with unknown HIV status. Factors associated with knowledge of serostatus are reported. HIV testing appears to be tied more to STI testing services than to primary care.
More strategies are needed that increase testing, including targeting partners of high-risk individuals, insuring receipt of test results, and increasing testing in primary care settings.
In E. coli, secA expression is regulated at the translational level by an upstream gene (secM) that encodes a presecretory protein. SecM contains a C-terminal sequence motif that induces a transient translation arrest. Inhibition of SecM membrane targeting prolongs the translation arrest and increases SecA synthesis by concomitantly altering the structure of the secM-secA mRNA. Here we show that the SecM signal peptide plays an essential role in this regulatory process by acting as a molecular timer that coordinates membrane targeting with the synthesis of the arrest motif. We found that signal peptide mutations that alter targeting kinetics and insertions or deletions that change the distance between the SecM signal peptide and the arrest motif perturb the balance between the onset and release of arrest that is required to regulate SecA synthesis. Furthermore, we found that the strength of the interaction between the ribosome and the SecM arrest motif is calibrated to ensure the release of arrest upon membrane targeting. Our results strongly suggest that several distinctive features of the SecM protein evolved as a consequence of constraints imposed by the ribosome and the Sec machinery.
membrane targeting; ribosome; SecM; signal peptide; translational regulation
It has been known for many years that the small lipoprotein Lpp, which is the most abundant protein in E. coli, exists in two forms. The “bound” form of the protein is tethered to the outer membrane (OM) by its N-terminal lipid moiety and covalently attached to the cell wall by its C-terminal lysine residue. The exact location of the “free” form, however, has never been determined. In this issue of Molecular Microbiology, Cowles et al. demonstrate that the free form of Lpp is an integral OM protein whose C-terminus is exposed on the cell surface. The new study provides the first example of a lipoprotein that has a dual localization and adds to a growing body of evidence that lipoproteins can span the OM despite the lack of an obvious transmembrane segment. Furthermore, the new results raise intriguing questions about the assembly of both lipoproteins and other types of OM proteins.
To examine methamphetamine use and its association with sexual behavior among young men who have sex with men.
Cross-sectional observational analysis.
Eight US cities.
As part of the Adolescent Trials Network for HIV/AIDS Interventions, adolescent boys and young men who have sex with men, aged 12 to 24 years, were recruited from social venues (eg, clubs, parks, and street corners) between January 3, 2005, and August 21, 2006, to complete a study survey.
Main Outcome Measures
Reported methamphetamine use in the past 90 days and reported sexual risk behavior compared with individuals reporting no hard drug use and individuals reporting hard drug use in the past 90 days.
Among 595 adolescent boys and young men, 64 reported recent methamphetamine use, and 444 reported no recent hard drug use (87 reported use of hard drugs other than methamphetamine). Recent methamphetamine use was associated with a history of sexually transmitted diseases (51.6%), 2 or more sex partners in the past 90 days (85.7%), sex with an injection drug user (51.6%), and sex with someone who has human immunodeficiency virus (32.8%) compared with individuals reporting no recent hard drug use (21.1%, 63.1%, 10.7%, and 11.1%, respectively; P<.05 for all [n=441]). Recent users of methamphetamine were more likely to have a history of homelessness (71.9%) and were less likely to be currently attending school (35.9%) compared with individuals reporting no recent hard drug use (28.4% and 60.4%, respectively; P<.001 for both).
Adolescent boys and young men who have sex with men and use methamphetamine seem to be at high risk for human immunodeficiency virus. Prevention programs among this age group should address issues like housing, polydrug use, and educational needs.
Autotransporters are a superfamily of virulence factors produced by Gram-negative bacteria that are comprised of an N-terminal extracellular domain (passenger domain) and a C-terminal β barrel domain (β domain) that resides in the outer membrane (OM). The β domain promotes the translocation of the passenger domain across the OM by an unknown mechanism. Available evidence indicates that an α-helical segment that spans the passenger domain-β domain junction is embedded inside the β domain at an early stage of assembly. Following its secretion, the passenger domain of the serine protease autotransporters of the Enterobacteriaceae (SPATEs) and the pertactin family of Bordetella pertussis autotransporters is released from the β domain through an intrabarrel autoproteolytic cleavage of the α-helical segment. Although the mutation of conserved residues that surround the cleavage site has been reported to impair both the translocation and cleavage of the passenger domain of a SPATE called Tsh, we show here that the mutation of the same residues in another SPATE (EspP) affects only passenger domain cleavage. Our results strongly suggest that the conserved residues are required to position the α-helical segment for the cleavage reaction and are not required to promote passenger domain secretion.
Many resource-limited countries rely on clinical and immunologic monitoring without routine virologic monitoring of HIV-infected children receiving highly active antiretroviral therapy (HAART). We assessed whether HIV viral load (VL) had independent predictive value in the presence of immunologic and clinical data for the occurrence of new World Health Organization (WHO) stage 3 or 4 events (WHO events) among HIV-infected children receiving HAART in Latin America.
The NICHD International Site Development Initiative (NISDI) Pediatric Protocol is an observational cohort study designed to describe HIV-related outcomes in infected children. Eligibility criteria for this analysis included perinatal infection, age <15 years, and continuous HAART for ≥6 months. Cox proportional hazards modeling was used to assess the time to new WHO events as a function of immunological status, VL, hemoglobin and potential confounding variables; laboratory tests repeated during the study were treated as time-varying predictors.
The mean follow-up was 2.5 years; new WHO events occurred in 16% of 584 children. In proportional hazards modeling, most recent VL > 5000 copies/mL was associated with a nearly doubled risk of developing a WHO event (adjusted hazard ratio=1.81, 95% CI 1.05–3.11; p=0.033), even after adjustment for CD4-defined immunosuppression, hemoglobin level, age and body mass index.
Routine virologic monitoring, using the WHO virologic failure threshold of 5,000 copies/mL, adds independent predictive value to immunologic and clinical assessments for identification of children receiving HAART who are at risk for significant HIV-related illness. To provide optimal care, periodic virologic monitoring should be considered for all settings providing HAART to children.
Pediatric HIV infection; viral load monitoring; Latin America
Background. Many resource-limited countries rely on clinical and immunological monitoring without routine virological monitoring for human immunodeficiency virus (HIV)-infected children receiving highly active antiretroviral therapy (HAART). We assessed whether HIV load had independent predictive value in the presence of immunological and clinical data for the occurrence of new World Health Organization (WHO) stage 3 or 4 events (hereafter, WHO events) among HIV-infected children receiving HAART in Latin America.
Methods. The NISDI (Eunice Kennedy Shriver National Institute of Child Health and Human Development International Site Development Initiative) Pediatric Protocol is an observational cohort study designed to describe HIV-related outcomes among infected children. Eligibility criteria for this analysis included perinatal infection, age <15 years, and continuous HAART for ≥6 months. Cox proportional hazards modeling was used to assess time to new WHO events as a function of immunological status, viral load, hemoglobin level, and potential confounding variables; laboratory tests repeated during the study were treated as time-varying predictors.
Results. The mean duration of follow-up was 2.5 years; new WHO events occurred in 92 (15.8%) of 584 children. In proportional hazards modeling, most recent viral load >5000 copies/mL was associated with a nearly doubled risk of developing a WHO event (adjusted hazard ratio, 1.81; 95% confidence interval, 1.05–3.11; P = .033), even after adjustment for immunological status defined on the basis of CD4 T lymphocyte value, hemoglobin level, age, and body mass index.
Conclusions. Routine virological monitoring using the WHO virological failure threshold of 5000 copies/mL adds independent predictive value to immunological and clinical assessments for identification of children receiving HAART who are at risk for significant HIV-related illness. To provide optimal care, periodic virological monitoring should be considered for all settings that provide HAART to children.
In this report we describe insights into the function of the ribosome tunnel that were obtained through an analysis of an unusual 25 residue N-terminal motif (EspP1-25) associated with the signal peptide of the E. coli EspP protein. It was previously shown that EspP1-25 inhibits signal peptide recognition by the signal recognition particle (SRP), and we now show that fusion of EspP1-25 to a cytoplasmic protein causes it to aggregate. We obtained two lines of evidence that both of these effects are attributable to the conformation of EspP1-25 inside the ribosome tunnel. First, we found that mutations in EspP1-25 that abolished its effects on protein targeting and protein folding altered the crosslinking of short nascent chains to ribosomal components. Second, we found that a mutation in L22 that distorts the tunnel mimicked the effects of the EspP1-25 mutations on protein biogenesis. Our results provide evidence that the conformation of a polypeptide inside the ribosome tunnel can influence protein folding under physiological conditions and suggest that ribosomal mutations might increase the solubility of at least some aggregation-prone proteins produced in E. coli.
protein folding; protein targeting; ribosome; signal peptide; translation
We present molecular dynamics (MD) simulation studies of the structural stability of an enclosed loop in the β domain of the E. coli O157:H7 autotransporter EspP. Our investigation revealed that in addition to its excellent resistance to thermal perturbations, EspP loop5(L5) also has remarkable mechanical stability against pulling forces along the membrane norm. These findings are consistent with the experimental report that EspP L5 helps to maintain the permeability barrier in the outer membrane(OM). In contrast to major secondary structure elements of globular proteins such as ubiquitin, whose resistance to thermal and mechanical perturbations depend mainly on backbone hydrogen bonds and hydrophobic interactions, the structural stability of EspP L5 can be attributed mainly to geometric constraints and side chain interactions dominated by hydrogen bonds. Examination of the B factors from available high resolution structures of membrane embedded β barrels (MEBBs) indicates that most of the enclosed loops have stable structures. This finding suggests that loops stabilized by geometric constraints and side chain interactions might be used more generally to restrict β barrel channels for various functional purposes.
β barrel; loop; stability; geometrical constraint; MD simulation; autotransporter; thermal factor; contact order
In Gram-negative bacteria, a variety of high molecular weight ‘exoproteins’ are translocated across the outer membrane (OM) via the two-partner secretion (TPS) pathway by interacting with a dedicated transporter. It is unclear, however, whether the translocation of exoproteins across the OM is coupled to their translocation across the inner membrane (IM). To address this question, we separated the production of an Escherichia coli O157:H7 exoprotein (OtpA) and its transporter (OtpB) temporally by placing otpA and otpB under the control of distinct regulatable promoters. We found that when both full-length and truncated forms of OtpA were expressed prior to OtpB, a significant fraction of the exoprotein was secreted. The results indicate that OtpA can be translocated into the periplasm and briefly remain secretion-competent. Furthermore, by engineering cysteine residues into OtpA and using disulphide bond formation as a reporter of periplasmic localization, we obtained additional evidence that the C-terminus of OtpA enters the periplasm before the N-terminus is translocated across the OM even when OtpA and OtpB are expressed simultaneously. Taken together, our results demonstrate that the translocation of a TPS exoprotein across the OM can occur independently from its translocation across the IM.
Interventions targeting multiple risk behaviors are needed for youth living with HIV (YLH). A randomized clinical trial compared Healthy Choices, a 4 session motivational intervention targeting two of three risk behaviors (HIV medication adherence, sexual risk behavior and substance use) to multidisciplinary specialty care alone. This paper presents intermediary outcomes available at 3-month follow-up, variables proposed to be precursors to behavior change (motivation, self-efficacy and depression).
YLH (N = 186) with at least one of the three problem behaviors were recruited from four sites in the Adolescent Trials Network (ATN) and one non-ATN site and were assessed at baseline and 3 months.
Of the 94 youth randomly assigned to the treatment condition, 84% received at least one session, 67% received at least two sessions, 56% received at least 3 sessions, and 49% completed all four sessions. In intent-to-treat analysis, only depression was significantly improved in the treatment group compared to controls. However, in per-protocol analysis, youth receiving at least two sessions of the intervention also showed significant improvements in motivational readiness to change compared to youth in the control condition.
Results suggest the potential benefits of clinic-based motivational interventions for YLH who access these interventions. Delivering interventions in the community using an outreach model may improve access. Analysis of subsequent time points will determine effects on actual behavior change.
This study investigates HIV positive adolescents’ health literacy and whether factors associated with health literacy in HIV-positive adults are associated with health literacy among HIV-positive adolescents.
Adolescents in this study were behaviorally and perinatally HIV-infected youth (N = 186) from five U.S. cities. Participants had a mean age of 20.5, and 49.5% were male.
Results and Conclusions
Contrary to findings for adult HIV-positive patients, among adolescents health literacy was not significantly associated with: medication adherence adjusting for age and education level; viral load; or self-efficacy to adhere to medication regimens. The only significant association was of health literacy with medical care received.
Practice implications are discussed.
HIV; Adolescent; Health Literacy