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1.  Reduced temperature-dependent thermal conductivity of magnetite thin films by controlling film thickness 
We report on the out-of-plane thermal conductivities of epitaxial Fe3O4 thin films with thicknesses of 100, 300, and 400 nm, prepared using pulsed laser deposition (PLD) on SiO2/Si substrates. The four-point probe three-omega (3-ω) method was used for thermal conductivity measurements of the Fe3O4 thin films in the temperature range of 20 to 300 K. By measuring the temperature-dependent thermal characteristics of the Fe3O4 thin films, we realized that their thermal conductivities significantly decreased with decreasing grain size and thickness of the films. The out-of-plane thermal conductivities of the Fe3O4 films were found to be in the range of 0.52 to 3.51 W/m · K at 300 K. For 100-nm film, we found that the thermal conductivity was as low as approximately 0.52 W/m · K, which was 1.7 to 11.5 order of magnitude lower than the thermal conductivity of bulk material at 300 K. Furthermore, we calculated the temperature dependence of the thermal conductivity of these Fe3O4 films using a simple theoretical Callaway model for comparison with the experimental data. We found that the Callaway model predictions agree reasonably with the experimental data. We then noticed that the thin film-based oxide materials could be efficient thermoelectric materials to achieve high performance in thermoelectric devices.
PMCID: PMC3938477  PMID: 24571956
Iron oxide (Fe3O4); Thermal conductivity; 2D thin films; 3-ω technique; Callaway model; In-plane and out-of-plane
2.  Correction: Prevention of Anti-microbial Peptide LL-37-Induced Apoptosis and ATP Release in the Urinary Bladder by a Modified Glycosaminoglycan 
PLoS ONE  2014;9(1):10.1371/annotation/0b7d0567-2fbd-4d32-84f1-9a0a9c290e70.
PMCID: PMC3888446
3.  Clinical Analysis of Blepharospasm and Apraxia of Eyelid Opening in Patients with Parkinsonism 
Background and Purpose
Blepharospasm (BSP) and apraxia of eyelid opening (AEO) have been reported as dystonia related with parkinsonism. However, systematic analysis of clinical characteristics of BSP and AEO in parkinsonism has been seldom reported. To investigate the clinical characteristics of BSP and AEO in parkinsonism and to find out the clinical significance to differentiate parkinsonism.
We enrolled 35 patients who had BSP with or without AEO out of 1113 patients with parkinsonism (913 IPD, idiopathic Parkinson's disease; 190 MSA, multiple system atrophy, 134 MSA-p, 56 MSA-c and 10 PSP, progressive supranuclear palsy). We subdivided MSA into MSA-p (predominantly parkinsonism) and MSA-c (predominantly cerebellar) according to the diagnostic criteria proposed by Quinn. We analyzed the clinical features of BSP and parkinsonism including onset age, onset interval to BSP, characteristics of BSP, presence of AEO, coexisted dystonias on the other body parts, severity of parkinsonism and relationship with levodopa treatment.
BSP with or without AEO were more frequently observed in atypical parkinsonism (PSP, 70%; MSA-p, 11.2%; MSA-c, 8.9%) than in IPD (0.9%). Reflex BSP was observed only in atypical parkinsonism (4 MSA-p, 1 MSA-c and 2 PSP). BSP preceding parkinsonism (Pre-BSP) was observed mainly in atypical parkinsonism (2 MSA-p, 1 MSA-c, 1 PSP and 1 IPD). The presence of AEO was more frequent in atypical parkinsonism than in IPD, but isolated AEO was not detected. BSP related to levodopa ('off' symptom or 'peak-dose' effect) were observed only in IPD.
Reflex BSP, Pre-BSP and the presence of AEO may be a unique feature of atypical parkinsonism. BSP related to levodopa might be representative of IPD. No differences were found in the clinical features of BSP between MSA-p and MSA-c.
PMCID: PMC2854921  PMID: 20396463
Blepharospasm; Apraxia of eyelid opening; Parkinsonism; Reflex blepharospasm
4.  Non-Invasive Imaging of Tumors by Monitoring Autotaxin Activity Using an Enzyme-Activated Near-Infrared Fluorogenic Substrate 
PLoS ONE  2013;8(11):e79065.
Autotaxin (ATX), an autocrine motility factor that is highly upregulated in metastatic cancer, is a lysophospholipase D enzyme that produces the lipid second messenger lysophosphatidic acid (LPA) from lysophosphatidylcholine (LPC). Dysregulation of the lysolipid signaling pathway is central to the pathophysiology of numerous cancers, idiopathic pulmonary fibrosis, rheumatoid arthritis, and other inflammatory diseases. Consequently, the ATX/LPA pathway has emerged as an important source of biomarkers and therapeutic targets. Herein we describe development and validation of a fluorogenic analog of LPC (AR-2) that enables visualization of ATX activity in vivo. AR-2 exhibits minimal fluorescence until it is activated by ATX, which substantially increases fluorescence in the near-infrared (NIR) region, the optimal spectral window for in vivo imaging. In mice with orthotopic ATX-expressing breast cancer tumors, ATX activated AR-2 fluorescence. Administration of AR-2 to tumor-bearing mice showed high fluorescence in the tumor and low fluorescence in most healthy tissues with tumor fluorescence correlated with ATX levels. Pretreatment of mice with an ATX inhibitor selectively decreased fluorescence in the tumor. Together these data suggest that fluorescence directly correlates with ATX activity and its tissue expression. The data show that AR-2 is a non-invasive and selective tool that enables visualization and quantitation of ATX-expressing tumors and monitoring ATX activity in vivo.
PMCID: PMC3835791  PMID: 24278115
5.  Prevention of Anti-microbial Peptide LL-37-Induced Apoptosis and ATP Release in the Urinary Bladder by a Modified Glycosaminoglycan 
PLoS ONE  2013;8(10):e77854.
Interstitial cystitis (IC), often referred to in combination with painful bladder syndrome, is a chronic inflammatory disease of the bladder. Current therapies primarily focus on replenishing urothelial glycosaminoglycan (GAG) layer using GAG analogs and managing pain with supportive therapies. However, the elusive etiology of IC and the lack of animal models to study the disease have been major hurdles developing more effective therapeutics. Previously, we showed an increased urinary concentration of antimicrobial peptide LL-37 in spina bifida patients and used LL-37 to develop a mouse model of cystitis that mimics important clinical findings of IC. Here we investigate (1) the molecular mechanism of LL-37 induced cystitis in cultured human urothelial cells and in mice, (2) the protective effects of GM-0111, a modified GAG, within the context of this mechanism, (3) the physiological and molecular markers that correlate with the severity of the inflammation, and (4) the protective effects of several GAGs using these biomarkers in our LL-37 induced cystitis model. We find that LL-37 quickly induces release of ATP and apoptosis in the urothelium. These changes can be inhibited by a chemically-modified GAG, GM-0111. Furthermore, we also find that GAG analogs provide varying degrees of protection against LL-37 challenge in mice. These findings suggest that GM-0111 and possibly GAG molecules prevent the development of cystitis by blocking the apoptosis and the concurrent release of ATP from the urothelium.
PMCID: PMC3813730  PMID: 24204996
6.  Does Carpal Tunnel Release Provide Long-Term Relief in Patients with Hemodialysis-Associated Carpal Tunnel Syndrome? 
Carpal tunnel syndrome (CTS) is a common complication in patients receiving long-term hemodialysis. In the short-term however, these patients are less likely to have pain relief and restoration of function after carpal tunnel release. However, it is unclear whether patients who have release for hemodialysis-associated CTS have differing persisting relief of symptoms compared with patients with idiopathic CTS.
We therefore compared (1) the severity of pain and level of function in patients who had release for hemodialysis-associated CTS with scores of patients who had release for idiopathic CTS, and (2) the operation-related complications.
We retrospectively reviewed 36 patients with CTS who were receiving hemodialysis and 54 patients with idiopathic CTS. Control subjects were matched for age, gender, and symptom severity. We obtained Boston Carpal Tunnel Questionnaire (BCTQ) scores preoperatively and at each followup. The minimum followup was 24 months (mean, 44.3 months; range, 24–90 months), although all comparisons were made at 2 years.
Two years after carpal tunnel release, the mean BCTQ-symptom (S) /BCTQ-function (F) scores improved from 3.3/2.1 to 2.1/2.1 in the hemodialysis-associated CTS group and from 3.2/2.3 to 1.4/1.4 in the idiopathic CTS group. All but six patients receiving hemodialysis had lower (better) BCTQ-S scores than their initial scores. Four patients had complications, all with hemodialysis-associated CTS: two had revision carpal tunnel releases and two had delayed wound healing. We observed no arteriovenous fistula-related complication.
Patients with hemodialysis-associated CTS seem to remain impaired, unlike patients with idiopathic CTS, but the majority of them might have much improved CTS-related symptoms at 2 years after carpal tunnel release.
Level of Evidence
Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
PMCID: PMC3830077  PMID: 22399438
7.  Direct observation of CD4 T cell morphologies and their cross-sectional traction force derivation on quartz nanopillar substrates using focused ion beam technique 
Nanoscale Research Letters  2013;8(1):332.
Direct observations of the primary mouse CD4 T cell morphologies, e.g., cell adhesion and cell spreading by culturing CD4 T cells in a short period of incubation (e.g., 20 min) on streptavidin-functionalized quartz nanopillar arrays (QNPA) using a high-content scanning electron microscopy method were reported. Furthermore, we first demonstrated cross-sectional cell traction force distribution of surface-bound CD4 T cells on QNPA substrates by culturing the cells on top of the QNPA and further analysis in deflection of underlying QNPA via focused ion beam-assisted technique.
PMCID: PMC3750221  PMID: 23875892
Cell traction force; Cell adhesion; CD4 T cell; Cell migration; Focused ion beam
8.  Customized Tracheostomy Cannula as a Therapeutic Adjunct in Tracheal Stenosis 
Case Reports in Otolaryngology  2013;2013:921365.
Tracheotomy is often successfully used to manage tracheal stenosis, as a temporizing measure prior to definitive treatment or a long-term remedy. In some patients, where a sizeable portion trachea is stenotic, the fixed arm of an ordinary tracheotomy tube may not be of sufficient length to satisfactorily maintain the distal tracheal lumen, and commercially available adjustable tubes may not be at hand in certain clinical settings. Herein, we describe a simple method of constructing a temporary tracheotomy tube with an adjustable distal arm, allowing custom fit at the patient bedside.
PMCID: PMC3638524  PMID: 23878755
9.  Recent Structural and Mechanistic Insights into Endplate Acetylcholine Receptors 
Voluntary movement mediated by skeletal muscle relies on endplate acetylcholine receptors (AChR) to detect nerve-released ACh and depolarize themuscle fiber. Recent structural and mechanistic studies of the endplate AChR have catalyzed a leap in our understanding of the molecular steps in this chemical-to-electrical transduction process. Studies of acetylcholine binding protein (AChBP) give insight into ACh recognition, the first step in activation of the AChR. An atomic structural model of the Torpedo AChR at a resolution of 0.4 nm, together with single-ion channel recording methods, allow tracing of the link between the agonist binding event and gating of the ion channel, as well as determination of how the channel moves when it opens to allow flow of cations. Structural models of the human AChR enable precise mapping of disease-causing mutations, while studies of the speed with which single AChR channels open and close cast light on pathogenic mechanisms.
PMCID: PMC3478106  PMID: 18567853
acetylcholine receptor; acetylcholine binding protein; agonist recognition; binding-gating coupling mechanism; congenital myasthenic syndrome
10.  Descending Thoracic Aorta to Bilateral Femoral Artery Bypass in a Hostile Abdomen 
Descending thoracic aorta to femoral artery bypass has been used as a remedial operation after aortic or axillofemoral graft failure or graft infection and other intra-abdominal pathologies not amenable to standard aortofemoral revascularization. It can avoid abdomen approach and has been known as a durable procedure with excellent long-term patency. We reported descending thoracic aorta to femoral artery bypass grafting for primary revascularization in a 55-year-old male with hostile abdominal conditions.
PMCID: PMC3413833  PMID: 22880173
Aorta, surgery; Bypass
11.  Overnight switch from ropinirole to transdermal rotigotine patch in patients with Parkinson disease 
BMC Neurology  2011;11:100.
A recent trial involving predominantly Caucasian subjects with Parkinson Disease (PD) showed switching overnight from an oral dopaminergic agonist to the rotigotine patch was well tolerated without loss of efficacy. However, no such data have been generated for Korean patients.
This open-label multicenter trial investigated PD patients whose symptoms were not satisfactorily controlled by ropinirole, at a total daily dose of 3 mg to 12 mg, taken as monotherapy or as an adjunct to levodopa. Switching treatment from oral ropinirole to transdermal rotigotine was carried out overnight, with a dosage ratio of 1.5:1. After a 28-day treatment period, the safety and tolerability of switching was evaluated. Due to the exploratory nature of this trial, the effects of rotigotine on motor and nonmotor symptoms of PD were analyzed in a descriptive manner.
Of the 116 subjects who received at least one treatment, 99 (85%) completed the 28-day trial period. Dose adjustments were required for 11 subjects who completed the treatment period. A total of 76 treatment-emergent adverse events (AEs) occurred in 45 subjects. No subject experienced a serious AE. Thirteen subjects discontinued rotigotine prematurely due to AEs. Efficacy results suggested improvements in both motor and nonmotor symptoms and quality of life after switching. Fifty-two subjects (46%) agreed that they preferred using the patch over oral medications, while 31 (28%) disagreed.
Switching treatment overnight from oral ropinirole to transdermal rotigotine patch, using a dosage ratio of 1.5:1, was well tolerated in Korean patients with no loss of efficacy.
Trial registration
This trial is registered with the Registry (NCT00593606).
PMCID: PMC3166898  PMID: 21831297
12.  Outcome of Video-assisted Thoracoscopic Surgery for Spontaneous Secondary Pneumothorax 
Conventional treatment (i.e. chest tube insertion and chemical pleurodesis) still remains standard for patients with secondary spontaneous pneumothorax because the risk of surgical bullectomy is deemed high in this subset. However, it has been suggested that surgical treatment using thoracoscopy may expedite postoperative recovery and, thus, may reduce hospital stay.
Materials and Methods
Retrospective review of 61 patients with secondary spontaneous pneumothorax, who underwent conventional treatment (n=39) or video-assisted thoracoscopic surgery (VATS) (n=22) between January 2007 and December 2009, was performed. Talc was used for chemical pleurodesis in both groups.
Hospital stay of conventional treatment group and VATS group was 14.2±14.2 days (4~58 days) and 10.6±5.8 days (5~32 days), respectively, with statistically significant difference (p=0.033). Recurrence rate of conventional treatment group was also significantly higher (12/39, 30%) compared to VATS group (1/22, 4.5%) (p=0.016).
In selected patients with secondary spontaneous pneumothorax with continuous air leak or inadequate lung expansion, thoracoscopic surgery with chemical pleurodesis using talc results in shorter hospital stay and lower recurrence rate compared to conventional approach.
PMCID: PMC3249307  PMID: 22263156
Pneumothorax; Thoracoscopy; Pleurodesis
13.  Left Transradial Coronary Angiography in a Patient With Dextrocardia 
Korean Circulation Journal  2010;40(11):601-603.
Although dextrocardia occurs rarely, the incidence of coronary artery disease is similar to the general population. Because of unfamiliarity with performing catheterization, transradial coronary angiography has seldom been performed in a patient with dextrocardia. We successfully performed left transradial coronary angiography in a patient with a right side heart using counter-directional torquing of the catheters and mirror-image angiographic angles.
PMCID: PMC3008833  PMID: 21217939
Dextrocardia; Coronary angiography
14.  A Novel Conus Snail Polypeptide Causes Excitotoxicity by Blocking Desensitization of AMPA Receptors 
Current biology : CB  2009;19(11):900-908.
Ionotropic glutamate receptors (iGluRs) are glutamate-gated ion channels that mediate excitatory neurotransmission in the central nervous system. Based on both molecular and pharmacological criteria, iGluRs have been divided into two major classes, the non-NMDA-class, which includes both AMPA and kainate subtypes of receptors, and the NMDA-class. One evolutionarily conserved feature of iGluRs is their desensitization in the continued presence of glutamate. Thus, when in a desensitized state, iGluRs can be bound to glutamate, yet the channel remains closed. However, the relevance of desensitization to nervous system function has remained enigmatic.
Here, we report the identification and characterization of a novel polypeptide (con-ikot-ikot) from the venom of a predatory marine snail Conus striatus that specifically disrupts the desensitization of AMPA receptors (AMPARs). The stoichiometry of con-ikot-ikot appears reminiscent of the proposed subunit organization of AMPARs, i.e., a dimer of dimers, suggesting that it acts as a molecular four-legged clamp that holds the AMPAR channel open. Application of con-ikot-ikot to hippocampal slices caused a large and rapid increase in resting AMPAR-mediated current leading to neuronal death.
Our findings provide insight into the mechanisms that regulate receptor desensitization, and demonstrate that in the arms race between prey and predators, evolution has selected for a toxin that blocks AMPAR desensitization, thus revealing the fundamental importance of desensitization for regulating neural function.
PMCID: PMC2722447  PMID: 19481459
15.  Detection and Trapping of Intermediate States Priming Nicotinic Receptor Channel Opening 
Nature  2009;459(7245):451-454.
In the course of synaptic transmission in the brain and periphery, acetylcholine receptors (AChRs) rapidly transduce a chemical signal into an electrical impulse. The speed of transduction owes in large part to rapid ACh association and dissociation, implying a binding site relatively non-selective for small cations; selective transduction has been supposed to originate from the ability of ACh, over that of other organic cations, to trigger the subsequent channel opening step. However transitions to and from the open state were shown to be similar for agonists with widely different efficacies.1,2,3 Here, by studying mutant AChRs, we find that the ultimate closed to open transition is agonist-independent and preceded by two primed closed states; the first primed state elicits brief openings, whereas the second elicits long-lived openings. Long-lived openings and the associated primed state are detected in the absence and presence of agonist, and exhibit the same kinetic signatures under both conditions. By covalently locking the agonist binding sites in the bound conformation, we find that each site initiates a priming step. Thus a change in binding site conformation primes the AChR for channel opening in a process that enables selective activation by ACh while maximizing speed and efficiency of the biological response.
PMCID: PMC2712348  PMID: 19339970
16.  Binding to gating transduction in nicotinic receptors: Cys-loop energetically couples to pre-M1 and M2-M3 regions 
The nicotinic acetylcholine receptor (AChR) transduces binding of nerve-released ACh into opening of an intrinsic ion channel, yet the intra-protein interactions behind transduction remain to be fully elucidated. Attention has focused on the region of the AChR where the β1-β2 and Cys-loops from the extracellular domain project into a cavity framed by residues preceding the first transmembrane domain (pre-M1) and the linker spanning transmembrane domains M2 and M3. Previous studies identified a principal transduction pathway in which the pre-M1 domain is coupled to the M2-M3 linker through the β1-β2 loop. Here we identify a parallel pathway in which the pre-M1 domain is coupled to the M2-M3 linker through the Cys-loop. Mutagenesis, single channel kinetic analyses and thermodynamic mutant cycle analyses reveal energetic coupling among αLeu 210 from the pre-M1 domain, αPhe 135 and αPhe 137 from the Cys-loop and αLeu 273 from the M2-M3 linker. Residues at equivalent positions of non-α-subunits show negligible coupling, indicating these inter-residue couplings are specific to residues in the α-subunit. Thus the extracellular β1-β2 and Cys-loops bridge the pre-M1 domain and M2-M3 linker to transduce agonist binding into channel gating.
PMCID: PMC2728446  PMID: 19279256
Cys-loop; binding to gating transduction; inter-residue coupling; Neural Excitability; Synapses; Glia: Cellular Mechanisms/2
17.  A Relationship between the Obstructive Sleep Apnea Syndrome and the Erythrocyte Sedimentation Rate 
The erythrocyte sedimentation rate (ESR) is a marker for inflammation, and it has been identified as a risk factor for atherothrombotic cardiovascular disease. The aim of this study was to determine the relationship between the plasma ESR level and nocturnal oxygen desaturation or other polysomnographic variables and to examine the role of obesity in patients with obstructive sleep apnea syndrome (OSAS).
This retrospective study included 72 patients with a diagnosis of OSAS who underwent overnight polysomnography and routine blood tests between July and December of 2005. We compared the plasma ESR level with the sum of all the polysomnographic variables and divided the patient group into obese and non-obese patients.
The mean ESR level was 8.45 mm/hr. There was a significant difference in the ESR level between genders (P<0.001). A significant correlation was found between the percentage of time spent at a SpO2 below 90% and the ESR level in the obese group (BMI ≥25, N=43, P=0.012). In addition, the ESR levels had a positive correlation with age in the obese group (P=0.002). However, there was no significant correlation with the percentage of time spent at a SpO2 below 90% in the whole group of patients and in the non-obese group (BMI <25, N=29). The ESR level showed no correlation with the other polysomnographic variables.
The duration of deoxygenation in obese patients with OSAS may be associated with the ESR level which is an independent predictor of cardiovascular disease.
PMCID: PMC2751876  PMID: 19784404
Blood sedimentation; Obstructive sleep apnea; Oximetry; Polysomnography
18.  Nicotinic Receptor Interloop Proline Anchors β1-β2 and Cys loops in Coupling Agonist Binding to Channel Gating 
The Journal of General Physiology  2008;132(2):265-278.
Nicotinic acetylcholine receptors (AChRs) mediate rapid excitatory synaptic transmission throughout the peripheral and central nervous systems. They transduce binding of nerve-released ACh into opening of an intrinsic channel, yet the structural basis underlying transduction is not fully understood. Previous studies revealed a principal transduction pathway in which αArg 209 of the pre-M1 domain and αGlu 45 of the β1–β2 loop functionally link the two regions, positioning αVal 46 of the β1–β2 loop in a cavity formed by αPro 272 through αSer 269 of the M2–M3 loop. Here we investigate contributions of residues within and proximal to this pathway using single-channel kinetic analysis, site-directed mutagenesis, and thermodynamic mutant cycle analysis. We find that in contributing to channel gating, αVal 46 and αVal 132 of the signature Cys loop couple energetically to αPro 272. Furthermore, these residues are optimized in both their size and hydrophobicity to mediate rapid and efficient channel gating, suggesting naturally occurring substitutions at these positions enable a diverse range of gating rate constants among the Cys-loop receptor superfamily. The overall results indicate that αPro 272 functionally couples to flanking Val residues extending from the β1–β2 and Cys loops within the ACh binding to channel opening transduction pathway.
PMCID: PMC2483337  PMID: 18663134
19.  One-Year Open-Label Study of Entacapone in Patients with Advanced Parkinson Disease 
Background and purpose
A carboxy-O-methyl transferase inhibitor entacapone has been introduced as an adjuvant drug for Parkinson disease (PD) patients. Although clinical trials reported beneficial role of entacapone, a long-term trial over 3 years failed to show significant effect. The goals of this study were to evaluate the clinical benefit and the efficacy of entacapone in an open clinical practice.
After the completion of a double-blind placebo-controlled entacapone study, 149 patients from 4 centers were included. Antiparkinsonian medications were optimized by the judgment of the neurologists in charge. The clinical global impression (CGI) scale was obtained at 6 months and 1 year after the initiation of entacapone treatment.
Of the 149 patients, 117 patients chose to try entacapone in an open-label fashion. Sixty-nine (59%) patients completed the 1-year trial. Twenty-nine patients discontinued entacpaone before 6 months, and 19 between 6 months and 1 year during trial. Twelve patients out of 48 patients discontinued entacapone because of its poor efficacy. The CGI scale was 3.9 (±1.5) at the beginning of the trial, 4.3 (±1.1) at 6 month, and 3.8 (±1.3) at 1 year, respectively. The CGI scale of those who discontinued between 6 month and 1 year was 3.4 (±1.7), which was worse, but insignificantly, than that of the continuer.
The dropout at 1 year of our study was very high at 41%. Even though entacapone is indicated for advanced PD patients with motor fluctuation, the fluctuators commonly have dyskinesia and mental symptoms, which can become more troublesome with entacapone. In the patients with advanced PD, the clinical efficacy and side effects should be carefully considered in a long-term use of entacapone.
PMCID: PMC2686863  PMID: 19513296
Parkinson disease; Entacapone; Long-term efficacy
20.  Invariant Aspartic Acid in Muscle Nicotinic Receptor Contributes Selectively to the Kinetics of Agonist Binding 
The Journal of General Physiology  2004;124(5):555-567.
We examined functional contributions of interdomain contacts within the nicotinic receptor ligand binding site using single channel kinetic analyses, site-directed mutagenesis, and a homology model of the major extracellular region. At the principal face of the binding site, the invariant αD89 forms a highly conserved interdomain contact near αT148, αW149, and αT150. Patch-clamp recordings show that the mutation αD89N markedly slows acetylcholine (ACh) binding to receptors in the resting closed state, but does not affect rates of channel opening and closing. Neither αT148L, αT150A, nor mutations at both positions substantially affects the kinetics of receptor activation, showing that hydroxyl side chains at these positions are not hydrogen bond donors for the strong acceptor αD89. However substituting a negative charge at αT148, but not at αT150, counteracts the effect of αD89N, demonstrating that a negative charge in the region of interdomain contact confers rapid association of ACh. Interpreted within the structural framework of ACh binding protein and a homology model of the receptor ligand binding site, these results implicate main chain amide groups in the domain harboring αW149 as principal hydrogen bond donors for αD89. The specific effect of αD89N on ACh association suggests that interdomain hydrogen bonding positions αW149 for optimal interaction with ACh.
PMCID: PMC2234004  PMID: 15504901
acetylcholine receptor; ligand binding site; single channel kinetics; hydrogen bond; structural model
21.  Naturally Occurring Mutations at the Acetylcholine Receptor Binding Site Independently Alter ACh Binding and Channel Gating 
The Journal of General Physiology  2002;120(4):483-496.
By defining functional defects in a congenital myasthenic syndrome (CMS), we show that two mutant residues, located in a binding site region of the acetylcholine receptor (AChR) epsilon subunit, exert opposite effects on ACh binding and suppress channel gating. Single channel kinetic analysis reveals that the first mutation, ɛN182Y, increases ACh affinity for receptors in the resting closed state, which promotes sequential occupancy of the binding sites and discloses rate constants for ACh occupancy of the nonmutant αδ site. Studies of the analogous mutation in the δ subunit, δN187Y, disclose rate constants for ACh occupancy of the nonmutant αɛ site. The second CMS mutation, ɛD175N, reduces ACh affinity for receptors in the resting closed state; occupancy of the mutant site still promotes gating because a large difference in affinity is maintained between closed and open states. ɛD175N impairs overall gating, however, through an effect independent of ACh occupancy. When mapped on a structural model of the AChR binding site, ɛN182Y localizes to the interface with the α subunit, and ɛD175 to the entrance of the ACh binding cavity. Both ɛN182Y and ɛD175 show state specificity in affecting closed relative to desensitized state affinities, suggesting that the protein chain harboring ɛN182 and ɛD175 rearranges in the course of receptor desensitization. The overall results show that key residues at the ACh binding site differentially stabilize the agonist bound to closed, open and desensitized states, and provide a set point for gating of the channel.
PMCID: PMC2229537  PMID: 12356851
congenital myasthenic syndrome; single channel kinetics; agonist binding; channel gating; mutation analysis

Results 1-21 (21)