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1.  Structure and Association of Human Lactoferrin Peptides with Escherichia coli Lipopolysaccharide 
An 11-amino-acid amphipathic synthetic peptide homologous to a helical region on helix 1 of human lactoferrin HLP-2 exhibited bactericidal activity against Escherichia coli serotype O111, whereas an analogue synthesized with Pro substituted for Met, HLP-6, had greatly reduced antimicrobial activity. The bactericidal activity of HLP-2 was 10-fold greater than that of HLP-6 in both buffer and growth medium by time-kill assays. These assays also showed a pronounced lag phase that was both concentration and time dependent and that was far greater for HLP-2 than for HLP-6. Both peptides, however, were shown to be equally efficient in destabilizing the outer membrane when the hydrophobic probe 1-N-phenylnaphthylamine was used and to have the same lipopolysaccharide (LPS) binding affinity, as shown by polymyxin B displacement. Circular dichroism (CD) spectroscopy was used to study the structure and the organization of the peptides in solution and upon interaction with E. coli LPS. In the presence of LPS, HLP-2 and HLP-6 were found to bind and adopt a β-strand conformation rather than an α-helix, as shown by nonimmobilized ligand interaction assay-CD spectroscopy. Furthermore, this assay was used to show that there is a time-dependent association of peptide that results in an ordered formation of peptide aggregates. The rate of interpeptide association was far greater in HLP-2 LPS than in HLP-6 LPS, which was consistent with the lag phase observed on the killing curves. These results allow us to propose a mechanism by which HLP-2 folds and self-assembles at the outer membrane surface before exerting its activity.
PMCID: PMC415569  PMID: 15155221
2.  High-level production of animal-free recombinant transferrin from saccharomyces cerevisiae 
Animal-free recombinant proteins provide a safe and effective alternative to tissue or serum-derived products for both therapeutic and biomanufacturing applications. While recombinant insulin and albumin already exist to replace their human counterparts in cell culture media, until recently there has been no equivalent for serum transferrin.
The first microbial system for the high-level secretion of a recombinant transferrin (rTf) has been developed from Saccharomyces cerevisiae strains originally engineered for the commercial production of recombinant human albumin (Novozymes' Recombumin® USP-NF) and albumin fusion proteins (Novozymes' albufuse®). A full-length non-N-linked glycosylated rTf was secreted at levels around ten-fold higher than from commonly used laboratory strains. Modification of the yeast 2 μm-based expression vector to allow overexpression of the ER chaperone, protein disulphide isomerase, further increased the secretion of rTf approximately twelve-fold in high cell density fermentation. The rTf produced was functionally equivalent to plasma-derived transferrin.
A Saccharomyces cerevisiae expression system has enabled the cGMP manufacture of an animal-free rTf for industrial cell culture application without the risk of prion and viral contamination, and provides a high-quality platform for the development of transferrin-based therapeutics.
PMCID: PMC3000842  PMID: 21083917
3.  Comparison of Human Immunodeficiency Virus Type 1-Specific Inhibitory Activities in Saliva and Other Human Mucosal Fluids▿  
Clinical and Vaccine Immunology  2006;13(10):1111-1118.
Several human mucosal fluids are known to possess an innate ability to inhibit human immunodeficiency virus type 1 (HIV-1) infection and replication in vitro. This study compared the HIV-1 inhibitory activities of several mucosal fluids, whole, submandibular/sublingual (sm/sl), and parotid saliva, breast milk, colostrum, seminal plasma, and cervicovaginal secretions, from HIV-1-seronegative donors by using a 3-day microtiter infection assay. A wide range of HIV-1 inhibitory activity was exhibited in all mucosal fluids tested, with some donors exhibiting high levels of activity while others showed significantly lower levels. Colostrum, whole milk, and whole saliva possessed the highest levels of anti-HIV-1 activity, seminal fluid, cervicovaginal secretions, and sm/sl exhibited moderate levels, and parotid saliva consistently demonstrated the lowest levels of HIV-1 inhibition. Fast protein liquid chromatography gel filtration studies revealed the presence of at least three distinct peaks of inhibitory activity against HIV-1 in saliva and breast milk. Incubation of unfractionated and fractionated whole saliva with antibodies raised against human lactoferrin (hLf), secretory leukocyte protease inhibitor (SLPI), and, to a lesser extent, MG2 (high-molecular-weight mucinous glycoprotein) reduced the HIV-1 inhibitory activity significantly. The results suggest that hLf and SLPI are two key components responsible for HIV-1 inhibitory activity in different mucosal secretions. The variation in HIV inhibitory activity between the fluids and between individuals suggests that there may be major differences in susceptibility to HIV infection depending both on the individual and on the mucosal fluid involved.
PMCID: PMC1595323  PMID: 16928883
4.  Meningococcal Transferrin-Binding Proteins A and B Show Cooperation in Their Binding Kinetics for Human Transferrin  
Infection and Immunity  2005;73(2):944-952.
Neisseria meningitidis, a causative agent of bacterial meningitis and septicemia, obtains transferrin-bound iron by expressing two outer membrane-located transferrin-binding proteins, TbpA and TbpB. A novel system was developed to investigate the interaction between Tbps and human transferrin. Copurified TbpA-TbpB, recombined TbpA-TbpB, and individual TbpA and TbpB were reconstituted into liposomes and fused onto an HPA chip (BIAcore). All preparations formed stable monolayers, which, with the exception of TbpB, could be regenerated by removing bound transferrin. The ligand binding properties of these monolayers were characterized with surface plasmon resonance and shown to be specific for human transferrin. Kinetic data for diferric human transferrin binding showed that recombined TbpA-TbpB had Ka and Kd values similar to those of copurified TbpA-TbpB. Individual TbpA and TbpB also displayed Ka values similar to those of copurified TbpA-TbpB, but their Kd values were one order of magnitude higher. Chemical cross-linking studies revealed that TbpA and TbpB, in the absence of human transferrin, formed large complexes with TbpA as the predominant species. Upon human transferrin binding, a complex was formed with a molecular mass corresponding to that of a TbpB-human transferrin heterodimer as well as a higher-molecular-mass complex of this heterodimer cross-linked to TbpA. This indicates that TbpA and TbpB form a functional meningococcal receptor complex in which there is cooperativity in the human transferrin binding kinetics. However, iron loss from the diferric human transferrin-TbpA-TbpB complex was not greater than that from human transferrin alone, suggesting that additional meningococcal transport components are involved in the process of iron removal.
PMCID: PMC546982  PMID: 15664936
5.  Development and Evaluation of Detection Systems for Staphylococcal Exfoliative Toxin A Responsible for Scalded-Skin Syndrome 
Journal of Clinical Microbiology  2001;39(6):2050-2054.
Staphylococcal scalded-skin syndrome is usually diagnosed clinically by its characteristic exfoliating rash. Isolation of Staphylococcus aureus from the patient further supports the diagnosis. Several detection systems have been developed to determine whether the isolated strain produces exfoliative toxin, but none are routinely available in hospital laboratories. In a novel approach, we used computer models to predict the structure of the exfoliative toxins based on other serine proteases and to identify surface epitopes for the production of antibodies that specifically bound the exfoliative toxin A (ETA) serotype. Several rapid immunologically based diagnostic tests for ETA were developed with these antibodies and compared with existing systems. Our results showed that Western blot analysis using these antibodies was in complete correlation with PCR, which has been validated against the “gold standard” mouse model. On the other hand, the double-antibody enzyme-linked immunosorbent assay (ELISA) and Ouchterlony immunodiffusion assay gave unacceptably high false-positive results due to interference by staphylococcal protein A. This problem was successfully overcome by the development of a F(ab′)2 fragment ELISA, which was rapid and reproducible and was as sensitive and specific as PCR and Western blot analysis. The F(ab′)2 fragment ELISA is superior to existing diagnostic systems because it is quantitative, which may be related to the severity of the condition, and can detect amounts of exfoliative toxin in the picogram range directly from serum. This is the first detection system with the potential to confirm the diagnosis of staphylococcal scalded-skin syndrome from a routine blood test within 3 h of presentation.
PMCID: PMC88087  PMID: 11376033
6.  Clinical, Microbial, and Biochemical Aspects of the Exfoliative Toxins Causing Staphylococcal Scalded-Skin Syndrome 
Clinical Microbiology Reviews  1999;12(2):224-242.
The exfoliative (epidermolytic) toxins of Staphylococcus aureus are the causative agents of the staphylococcal scalded-skin syndrome (SSSS), a blistering skin disorder that predominantly affects children. Clinical features of SSSS vary along a spectrum, ranging from a few localized blisters to generalized exfoliation covering almost the entire body. The toxins act specifically at the zona granulosa of the epidermis to produce the characteristic exfoliation, although the mechanism by which this is achieved is still poorly understood. Despite the availability of antibiotics, SSSS carries a significant mortality rate, particularly among neonates with secondary complications of epidermal loss and among adults with underlying diseases. The aim of this article is to provide a comprehensive review of the literature spanning more than a century and to cover all aspects of the disease. The epidemiology, clinical features, potential complications, risk factors, susceptibility, diagnosis, differential diagnoses, investigations currently available, treatment options, and preventive measures are all discussed in detail. Recent crystallographic data on the toxins has provided us with a clearer and more defined approach to studying the disease. Understanding their mode of action has important implications in future treatment and prevention of SSSS and other diseases, and knowledge of their specific site of action may provide a useful tool for physiologists, dermatologists, and pharmacologists.
PMCID: PMC88916  PMID: 10194458
7.  Receptor-Mediated Recognition and Uptake of Iron from Human Transferrin by Staphylococcus aureus and Staphylococcus epidermidis 
Infection and Immunity  1998;66(8):3591-3596.
Staphylococcus aureus and Staphylococcus epidermidis both recognize and bind the human iron-transporting glycoprotein, transferrin, via a 42-kDa cell surface protein receptor. In an iron-deficient medium, staphylococcal growth can be promoted by the addition of human diferric transferrin but not human apotransferrin. To determine whether the staphylococcal transferrin receptor is involved in the removal of iron from transferrin, we employed 6 M urea–polyacrylamide gel electrophoresis, which separates human transferrin into four forms (diferric, monoferric N-lobe, and monoferric C-lobe transferrin and apotransferrin). S. aureus and S. epidermidis but not Staphylococcus saprophyticus (which lacks the transferrin receptor) converted diferric human transferrin into its apotransferrin form within 30 min. During conversion, iron was removed sequentially from the N lobe and then from the C lobe. Metabolic poisons such as sodium azide and nigericin inhibited the release of iron from human transferrin, indicating that it is an energy-requiring process. To demonstrate that this process is receptor rather than siderophore mediated, we incubated (i) washed staphylococcal cells and (ii) the staphylococcal siderophore, staphyloferrin A, with porcine transferrin, a transferrin species which does not bind to the staphylococcal receptor. While staphyloferrin A removed iron from both human and porcine transferrins, neither S. aureus nor S. epidermidis cells could promote the release of iron from porcine transferrin. In competition binding assays, both native and recombinant N-lobe fragments of human transferrin as well as a naturally occurring human transferrin variant with a mutation in the C-lobe blocked binding of 125I-labelled transferrin. Furthermore, the staphylococci removed iron efficiently from the iron-loaded N-lobe fragment of human transferrin. These data demonstrate that the staphylococci efficiently remove iron from transferrin via a receptor-mediated process and provide evidence to suggest that there is a primary receptor recognition site on the N-lobe of human transferrin.
PMCID: PMC108390  PMID: 9673237
8.  Structure-Function Relationship of Antibacterial Synthetic Peptides Homologous to a Helical Surface Region on Human Lactoferrin against Escherichia coli Serotype O111 
Infection and Immunity  1998;66(6):2434-2440.
Lactoferricin includes an 11-amino-acid amphipathic alpha-helical region which is exhibited on the outer surface of the amino-terminal lobe of lactoferrin. Synthetic peptides homologous to this region exhibited potent antibacterial activity against a selected range of both gram-negative and gram-positive bacteria. An analog synthesized with methionine substituted for proline at position 26, which is predicted to disrupt the helical region, abolished antibacterial activity against Escherichia coli and considerably reduced antibacterial activity against Staphylococcus aureus and an Acinetobacter strain. The mode of action of human lactoferrin peptide (HLP) 2 against E. coli serotype O111 (NCTC 8007) was established by using flow cytometry, surface plasmon resonance, and transmission electron microscopy. Flow cytometry was used to monitor membrane potential, membrane integrity, and metabolic processes by using the fluorescent probes bis-1,3-(dibutylbarbituric acid)-trimethine oxonol, propidium iodide, and carbonyl cyanide m-chlorophenylhydrazone, respectively. HLP 2 was found to act at the cell membrane, causing complete loss of membrane potential after 10 min and of membrane integrity within 30 min, with irreversible damage to the cell as shown by rapid loss of viability. The number of particles, measured by light scatter on the flow cytometer, dropped significantly, showing that bacterial lysis resulted. The peptide was shown to bind to E. coli O111 lipopolysaccharide by using surface plasmon resonance. Transmission electron microscopy revealed bacterial distortion, with the outer membrane becoming detached from the inner cytoplasmic membrane. We conclude that HLP 2 causes membrane disruption of the outer membrane, resulting in lysis, and that structural considerations are important for antibacterial activity.
PMCID: PMC108221  PMID: 9596699

Results 1-8 (8)