Microfluidic viscometer by acoustic streaming transducers.

Measurement of fluid viscosity represents a huge need for many biomedical and materials processing applications. Sample fluids containing DNA, antibodies, protein-based drugs, and even cells have become important therapeutic options. The physical properties, including viscosity, of these biologics are critical factors in the optimization of the biomanufacturing processes and delivery of therapeutics to patients. Here we demonstrate an acoustic microstreaming platform termed as microfluidic viscometer by acoustic streaming transducers (µVAST) that induces fluid transport from second-order microstreaming to measure viscosity. Validation of our platform is achieved with different glycerol content mixtures to reflect different viscosities and shows that viscosity can be estimated based on the maximum speed of the second-order acoustic microstreaming. The µVAST platform requires only a small volume of fluid sample (∼1.2 µL), which is 16-30 times smaller than that of commercial viscometers. In addition, µVAST can be scaled up for ultra-high throughput measurements of viscosity. Here we demonstrate 16 samples within 3 seconds, which is an attractive feature for automating the process flows in drug development and materials manufacturing and production.

15N-Detected TROSY NMR experiments to study large disordered proteins in high-field magnets.

Intrinsically disordered regions (IDRs) of proteins are critical in the regulation of biological processes but difficult to study structurally. Nuclear magnetic resonance (NMR) is uniquely equipped to provide structural information on IDRs at atomic resolution; however, existing NMR methods often pose a challenge for large molecular weight IDRs. Resonance assignment of IDRs using 15ND-detection was previously demonstrated and shown to overcome some of these limitations. Here, we improve the methodology by overcoming the need for deuterated buffers and provide better sensitivity and resolution at higher magnetic fields and physiological salt concentrations using transverse relaxation optimized spectroscopy (TROSY). Finally, large disordered regions with low sequence complexity can be assigned efficiently using these new methods as demonstrated by achieving near complete assignment of the 398-residue N-terminal IDR of the transcription factor NFAT1 harboring 18% prolines.

Clinical Profile of Coronavirus Disease 2019 Comparing the First and Second Waves: A Single-Center Study from North India.

Background and Objectives: Severe acute respiratory syndrome coronavirus 2, caused by the novel coronavirus disease 2019 (COVID-19), led to a devastating pandemic that hit majority of the countries globally in a wave-like pattern. The characteristics of the disease varied in different geographical areas and different populations. This study highlights the epidemiological and clinical characteristics of COVID-19 during two major waves in North India. Materials and Methods: Clinical characteristics and outcomes of all COVID-19-reverse transcription-polymerase chain reaction-positive patients, admitted from March 2020 to June 2021, to a tertiary care center in North India, were studied retrospectively. Results: During this period, total of 5652 patients were diagnosed having COVID. Patients who were incidentally diagnosed as COVID-positive (n=667) with other unrelated comorbid conditions and patients admitted under level 1 facility (n=1655; 1219 from first and 436 from second wave) were excluded from final analysis. Males were most commonly affected in both waves, with male to female ratio 4:1 in first and 3:1 in second wave. First wave had significantly more people with co-morbidities like diabetes mellitus and hypertension (P=0.001), whereas younger age group (age <40 years) were significantly more affected in second wave (P= 0.000). Fever was the most common presenting complaint in both waves, followed by cough and breathlessness. Patients during first wave had more severe disease at presentation and high mortality compared to the second wave. Conclusion: Majority of the patients with COVID-19 infection presenting to our hospital were young during the second wave. Fever was noted as presenting manifestation. Mortality was low during the second wave as compared to the first wave, likely to be due to proper protocol-based treatment resulting in better outcomes.

Various Factors that are Causing Difference in Prevalence of Coronary Risk Factors among Siblings.

BACKGROUND AND AIM: Coronary artery disease (CAD) is one of the predominant types of cardiovascular disease (CVD). The aim of present study was to study various factors that are causing difference in prevalence of coronary risk factors among siblings. MATERIALS AND METHODS: This cross-sectional study was conducted in Dayanand Medical College and Hospital, among the healthy individuals (not known CAD) attending regular health care outpatient department (OPD) and their siblings over a period of 1½ years. All individuals coming for regular health checkup (not known CAD) of age more than 30 years or above and their siblings (with or without known CAD). RESULTS: This was a cross-sectional study, conducted among 100 pairs of healthy siblings (not known cases of CAD) who came for health checkup at health center of Dayanand Medical College and Hospital, a tertiary care hospital in North India. Prevalence of obesity was more in siblings living in urban area than their counter siblings living in rural area, but it was statistically insignificant. Six had impaired fasting blood sugar (FBS) and two were diabetic. Among their siblings living in urban area, 21 were nondiabetic, 10 had impaired FBS, and seven were diabetic. This correlation was statistically significant with p-value of 0.02. Among the CAD negative, out of 23 subjects, two subjects (9.0%) had heavy stress level, while remaining four subjects (17.0%) and 17 subjects (74.0%) had light and moderate stress levels, respectively. Among the CAD negative, out of 23 subjects, 10 subjects (43.0%) had high stress level, while remaining zero subject (0%) and 13 subjects (57.0%) had light and moderate stress levels, respectively. Significant results were obtained while comparing the CAD findings of subjects divided on the basis of stress level. CONCLUSION: In our study, among siblings (CAD positive and CAD negative), significant results were obtained for residence, socioeconomic class, physical activity, stress levels, smoking, waist-to-hip ratio (WHR), and diabetes, that is, all these factors have correlation in increasing CAD among siblings.

Diabetes Mellitus Increases the Risk of Significant Hepatic Fibrosis in Patients With Non-alcoholic Fatty Liver Disease.

Background: Diabetes mellitus is associated with an increased risk of development of non-alcoholic fatty liver disease (NAFLD). However, the risk posed by diabetes mellitus in progression of liver disease is uncertain. This study compared the severity of hepatic fibrosis in patients with NAFLD with and without diabetes mellitus. Methods: Consecutive adult patients with NAFLD undergoing transient elastography [FibroScan Touch 502 (Echosens, Paris, France)] at a tertiary care center in north India were analyzed for severity of hepatic fibrosis. The aspartate aminotransferase (AST) to platelet ratio index (APRI), fibrosis index based on 4 factors (FIB-4), and NAFLD Fibrosis Score (NFS) were calculated. The degree of hepatic fibrosis as determined by FibroScan and non-invasive serum fibrosis models in patients with and without diabetes mellitus were compared. Results: A total of two hundred patients [118 (59%) males, mean age 50.30 ± 11.13 years] were enrolled. Significant hepatic fibrosis was present in 86 (43%) patients [mean age 50.66 ± 10.96 years, 56 (65.11%) males]. The mean FibroScan, APRI, FIB-4, and NFS scores were 9.86 ± 2.97, 0.75 ± 0.47, 2.41 ± 1.41 and -0.24 ± 1.43 in patients with diabetes compared to 5.31 ± 1.09, 0.49 ± 0.27, 1.55 ± 0.85, and -2.12 ± 1.88 in patients without diabetes, respectively (P=<0.0001). There was a fair correlation between FibroScan and non-invasive serum fibrosis models (P=<0.0001). Conclusion: Presence of diabetes increases the risk of significant hepatic fibrosis in patients with NAFLD. FIB-4 correlates fairly with FibroScan in patients with diabetes and can be used as a screening tool to detect significant hepatic fibrosis.

Anemia and Nutritional Status in Tuberculosis Patients.

INTRODUCTION: Anemia is a common complication of pulmonary tuberculosis (TB). Nutritional deficiency and malabsorption syndrome can deepen the severity of anemia. The aim of the present study was to study anemia and nutritional status in patients with TB at a tertiary care center. MATERIALS AND METHODS: All patients diagnosed with TB (pulmonary and extrapulmonary), registered withRevised National TB Control Programme (RNTCP), taking DOTS regimen, attending the outpatient department as well as those admitted in the medicine and chest units of a tertiary care hospital, were enrolled in the present study. RESULTS: Anemia was more common between the age groups of 51 and 60 years, with distribution of males (87 [58%]), patients with diabetes (49 [32%]), and hypertensive patients (29 [19.3%]). In our study, 48 (85.7%) out of 56 patients diagnosed with extrapulmonary TB were found to have anemia; similarly, 77 (88.5%) out of 87 patients diagnosed to have pulmonary TB were anemic. Anemia of chronic disease (128 [97.17%]) was higher when compared to that of those with iron-deficiency anemia (3 [2.29%]). According to body mass index (BMI), 135 (90%) patients were underweight; according to mid-arm circumference (MAC), 131 (87.3%) patients had severe malnutrition; and according to waist-hip ratio [WHR], 96 (64%) patients were underweight. CONCLUSION: Anemia was common in males and alcoholics, and there was a high prevalence of anemia of chronic disease. In addition, anemia was associated with high erythrocyte sedimentation rate and C-reactive protein. High proportions of TB patients (pulmonary and extrapulmonary) were classified as underweight and malnourished on the basis of different parameters (BMI, MAC, and WHR); in addition, the degree of malnutrition was higher in patients with anemia than in those without.

Comparison of Tocilizumab and High-dose Methylprednisolone Pulse on Outcomes in Severe Corona Virus Disease-2019: TAME-COVID, a Retrospective Multicentric Study.

BACKGROUND: India recently encountered fierce second wave of coronavirus disease (COVID-19), and scarcity of novel medications added to the management challenges. Various studies have highlighted the effectiveness of tocilizumab and high-dose steroids in severe COVIDs, but none has compared their efficacy. MATERIALS AND METHODS: This retrospective multi-centric analysis compares intravenous tocilizumab (8 mg/kg/day, maximum dose-800 mg), and intravenous Methylprednisolone Pulse (MPS-1 g/day for 3 days) in severe COVID-19. Both the groups had additionally received the standard of care COVID treatment as per protocol. Outcomes were assessed at 30 days. RESULTS: A total of 336 patients, with 249 receiving MPS and 87 receiving tocilizumab were compared. Majority of these were males (72.9%) with a mean age of 57.4 ± 13.6 years. Diabetes was the most common comorbidity. Patients in both groups had comparable age distribution, comorbidities, presenting mean-arterial pressures, d-Dimer levels, serum ferritin, serum leukocyte-dehydrogenase, and procalcitonin. However, the tocilizumab group had more number of males, higher incidence of coronary artery disease, more tachypnea and leukocytosis, more number of patients with severe acute respiratory disease syndrome (PaO2/FiO2 ratio <100), and higher C-reactive protein levels at presentation. Both groups had comparable adverse events' profile. Tocilizumab group had lesser requirement of invasive ventilation than MPS group (17% vs. 29%, P = 0.038), however mortality at the end of 30 days follow-up was similar (36% vs. 34% respectively; P = 0.678). CONCLUSIONS: Tocilizumab decreased the need for invasive ventilation in severe COVID-19; however, it did not translate to improved survival. A planned prospective randomized study is recommended in this respect to compare their efficacy.

Local Deuteration Enables NMR Observation of Methyl Groups in Proteins from Eukaryotic and Cell-Free Expression Systems.

Therapeutically relevant proteins such as GPCRs, antibodies and kinases face clear limitations in NMR studies due to the challenges in site-specific isotope labeling and deuteration in eukaryotic expression systems. Here we describe an efficient and simple method to observe the methyl groups of leucine residues in proteins expressed in bacterial, eukaryotic or cell-free expression systems without modification of the expression protocol. The method relies on simple stereo-selective 13 C-labeling and deuteration of leucine that alleviates the need for additional deuteration of the protein. The spectroscopic benefits of "local" deuteration are examined in detail through Forbidden Coherence Transfer (FCT) experiments and simulations. The utility of this labeling method is demonstrated in the cell-free synthesis of bacteriorhodopsin and in the insect-cell expression of the RRM2 domain of human RBM39.

Alkyne-Bridged α-Conotoxin Vc1.1 Potently Reverses Mechanical Allodynia in Neuropathic Pain Models.

Several Conus-derived venom peptides are promising lead compounds for the management of neuropathic pain, with α-conotoxins being of particular interest. Modification of the interlocked disulfide framework of α-conotoxin Vc1.1 has been achieved using on-resin alkyne metathesis. Although introduction of a metabolically stable alkyne motif significantly disrupts backbone topography, the structural modification generates a potent and selective GABAB receptor agonist that inhibits Cav2.2 channels and exhibits dose-dependent reversal of mechanical allodynia in a behavioral rat model of neuropathic pain. The findings herein support the hypothesis that analgesia can be achieved via activation of GABABRs expressed in dorsal root ganglion (DRG) sensory neurons.

Chemoradiation in locally advanced Ca Cx: Effect on NGAL levels.

INTRODUCTION: Neutrophil gelatinase-associated lipocalin (NGAL) has been reported to be unregulated in many cancers and to suppress tumor suppressor genes like p53 leading to cell proliferation. Studies to report its relationship with carcinoma cervix (Ca Cx) are still scant. MATERIALS AND METHODS: Serum NGAL levels were analyzed in 30 patients of histopathologically proven locally advanced Ca Cx at the time of diagnosis and 3 weeks after standard chemoradiation by enzyme-linked immunosorbent assay. These patients underwent either brachytherapy or supplementary external beam radiotherapy (EBRT) depending on the response of treatment. The results were analyzed statistically by applying Student's paired t-test. RESULTS: No statistically significant difference (P > 0.05) was observed in patients of Ca Cx before and after treatment or when compared stage wise, histopathological grade wise, or response wise. But the levels were found to increase when duration of treatment was ≥8 weeks (P = 0.040) and to decrease significantly when duration of treatment was <8 weeks (P = 0.0052). The NGAL levels also increased significantly after treatment in patients who received EBRT and supplementary radiotherapy (P = 0.019) while the pre- and post-treatment difference in NGAL levels was not statistically significant in patients who received EBRT + intracavitary brachytherapy (P > 0.05). CONCLUSION: As the duration as well as modality of treatment is quite important in Ca Cx, shorter duration associated with better results and lower NGAL levels, NGAL might prove to be a useful biomarker although further studies are needed to support the claim.

Aromatic 19F-13C TROSY: a background-free approach to probe biomolecular structure, function, and dynamics.

Atomic-level information about the structure and dynamics of biomolecules is critical for an understanding of their function. Nuclear magnetic resonance (NMR) spectroscopy provides unique insights into the dynamic nature of biomolecules and their interactions, capturing transient conformers and their features. However, relaxation-induced line broadening and signal overlap make it challenging to apply NMR spectroscopy to large biological systems. Here we took advantage of the high sensitivity and broad chemical shift range of 19F nuclei and leveraged the remarkable relaxation properties of the aromatic 19F-13C spin pair to disperse 19F resonances in a two-dimensional transverse relaxation-optimized spectroscopy spectrum. We demonstrate the application of 19F-13C transverse relaxation-optimized spectroscopy to investigate proteins and nucleic acids. This experiment expands the scope of 19F NMR in the study of the structure, dynamics, and function of large and complex biological systems and provides a powerful background-free NMR probe.

Hypocalcemia Presenting as Life Threatening Torsades de Pointes with Prolongation of QTc Interval.

Torsades de pointes with prolonged QTc interval is a form of ventricular tachycardia. Many predisposing factors have been identified and hypocalcemia is among the rare ones. Our case illustrates that though rare, hypocalcemia might manifest as torsades de pointes with prolongation of QTc interval. Early diagnosis and management of dyselectrolytemia can prevent these patients from catastrophic torsades de pointes.

15N detection harnesses the slow relaxation property of nitrogen: Delivering enhanced resolution for intrinsically disordered proteins.

Studies over the past decade have highlighted the functional significance of intrinsically disordered proteins (IDPs). Due to conformational heterogeneity and inherent dynamics, structural studies of IDPs have relied mostly on NMR spectroscopy, despite IDPs having characteristics that make them challenging to study using traditional 1H-detected biomolecular NMR techniques. Here, we develop a suite of 3D 15N-detected experiments that take advantage of the slower transverse relaxation property of 15N nuclei, the associated narrower linewidth, and the greater chemical shift dispersion compared with those of 1H and 13C resonances. The six 3D experiments described here start with aliphatic 1H magnetization to take advantage of its higher initial polarization, and are broadly applicable for backbone assignment of proteins that are disordered, dynamic, or have unfavorable amide proton exchange rates. Using these experiments, backbone resonance assignments were completed for the unstructured regulatory domain (residues 131-294) of the human transcription factor nuclear factor of activated T cells (NFATC2), which includes 28 proline residues located in functionally important serine-proline (SP) repeats. The complete assignment of the NFATC2 regulatory domain enabled us to study phosphorylation of NFAT by kinase PKA and phosphorylation-dependent binding of chaperone protein 14-3-3 to NFAT, providing mechanistic insight on how 14-3-3 regulates NFAT nuclear translocation.

8-Mercaptoguanine Derivatives as Inhibitors of Dihydropteroate Synthase.

Dihydropteroate synthase (DHPS) is an enzyme of the folate biosynthesis pathway, which catalyzes the formation of 7,8-dihydropteroate (DHPt) from 6-hydroxymethyl-7,8-dihydropterin pyrophosphate (DHPPP) and para-aminobenzoic acid (pABA). DHPS is the long-standing target of the sulfonamide class of antibiotics that compete with pABA. In the wake of sulfa drug resistance, targeting the structurally rigid (and more conserved) pterin site has been proposed as an alternate strategy to inhibit DHPS in wild-type and sulfa drug resistant strains. Following the work on developing pterin-site inhibitors of the adjacent enzyme 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase (HPPK), we now present derivatives of 8-mercaptoguanine, a fragment that binds weakly within both enzymes, and quantify sub-µm binding using surface plasmon resonance (SPR) to Escherichia coli DHPS (EcDHPS). Eleven ligand-bound EcDHPS crystal structures delineate the structure-activity relationship observed providing a structural framework for the rational development of novel, substrate-envelope-compliant DHPS inhibitors.

CDK4/6 Inhibition Augments Antitumor Immunity by Enhancing T-cell Activation.

Immune checkpoint blockade, exemplified by antibodies targeting the PD-1 receptor, can induce durable tumor regressions in some patients. To enhance the efficacy of existing immunotherapies, we screened for small molecules capable of increasing the activity of T cells suppressed by PD-1. Here, we show that short-term exposure to small-molecule inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6) significantly enhances T-cell activation, contributing to antitumor effects in vivo, due in part to the derepression of NFAT family proteins and their target genes, critical regulators of T-cell function. Although CDK4/6 inhibitors decrease T-cell proliferation, they increase tumor infiltration and activation of effector T cells. Moreover, CDK4/6 inhibition augments the response to PD-1 blockade in a novel ex vivo organotypic tumor spheroid culture system and in multiple in vivo murine syngeneic models, thereby providing a rationale for combining CDK4/6 inhibitors and immunotherapies.Significance: Our results define previously unrecognized immunomodulatory functions of CDK4/6 and suggest that combining CDK4/6 inhibitors with immune checkpoint blockade may increase treatment efficacy in patients. Furthermore, our study highlights the critical importance of identifying complementary strategies to improve the efficacy of immunotherapy for patients with cancer. Cancer Discov; 8(2); 216-33. ©2017 AACR.See related commentary by Balko and Sosman, p. 143See related article by Jenkins et al., p. 196This article is highlighted in the In This Issue feature, p. 127.

Distribution and kinetics of the Kv1.3-blocking peptide HsTX1[R14A] in experimental rats.

The peptide HsTX1[R14A] is a potent and selective blocker of the voltage-gated potassium channel Kv1.3, which is a highly promising target for the treatment of autoimmune diseases and other conditions. In order to assess the biodistribution of this peptide, it was conjugated with NOTA and radiolabelled with copper-64. [64Cu]Cu-NOTA-HsTX1[R14A] was synthesised in high radiochemical purity and yield. The radiotracer was evaluated in vitro and in vivo. The biodistribution and PET studies after intravenous and subcutaneous injections showed similar patterns and kinetics. The hydrophilic peptide was rapidly distributed, showed low accumulation in most of the organs and tissues, and demonstrated high molecular stability in vitro and in vivo. The most prominent accumulation occurred in the epiphyseal plates of trabecular bones. The high stability and bioavailability, low normal-tissue uptake of [64Cu]Cu-NOTA-HsTX1[R14A], and accumulation in regions of up-regulated Kv channels both in vitro and in vivo demonstrate that HsTX1[R14A] represents a valuable lead for conditions treatable by blockade of the voltage-gated potassium channel Kv1.3. The pharmacokinetics shows that both intravenous and subcutaneous applications are viable routes for the delivery of this potent peptide.

Reinvestigation of the biological activity of d-allo-ShK protein.

ShK toxin from the sea anemone Stichodactyla helianthus is a 35-residue protein that binds to the Kv1.3 ion channel with high affinity. Recently we determined the X-ray structure of ShK toxin by racemic crystallography, in the course of which we discovered that d-ShK has a near-background IC50 value ∼50,000 times lower than that of the l-ShK toxin. This lack of activity was at odds with previously reported results for an ShK diastereomer designated d-allo-ShK, for which significant biological activity had been observed in a similar receptor-blocking assay. As reported, d-allo-ShK was made up of d-amino acids, but with retention of the natural stereochemistry of the chiral side chains of the Ile and Thr residues, i.e. containing d-allo-Ile and d-allo-Thr along with d-amino acids and glycine. To understand its apparent biological activity, we set out to chemically synthesize d-allo-ShK and determine its X-ray structure by racemic crystallography. Using validated allo-Thr and allo-Ile, both l-allo-ShK and d-allo-ShK polypeptide chains were prepared by total chemical synthesis. Neither the l-allo-ShK nor the d-allo-ShK polypeptides folded, whereas both l-ShK and d-ShK folded smoothly under the same conditions. Re-examination of NMR spectra of the previously reported d-allo-ShK protein revealed that diagnostic Thr and Ile signals were the same as for authentic d-ShK. On the basis of these results, we conclude that the previously reported d-allo-ShK was in fact d-ShK, the true enantiomer of natural l-ShK toxin, and that the apparent biological activity may have arisen from inadvertent contamination with trace amounts of l-ShK toxin.

Structure and activity of contryphan-Vc2: Importance of the d-amino acid residue.

In natural proteins and peptides, amino acids exist almost invariably as l-isomers. There are, however, several examples of naturally-occurring peptides containing d-amino acids. In this study we investigated the role of a naturally-occurring d-amino acid in a small peptide identified in the transcriptome of a marine cone snail. This peptide belongs to a family of peptides known as contryphans, all of which contain a single d-amino acid residue. The solution structure of this peptide was solved by NMR, but further investigations with molecular dynamics simulations suggest that its solution behaviour may be more dynamic than suggested by the NMR ensemble. Functional tests in mice uncovered a novel bioactivity, a depressive phenotype that contrasts with the hyperactive phenotypes typically induced by contryphans. Trp3 is important for bioactivity, but this role is independent of the chirality at this position. The d-chirality of Trp3 in this peptide was found to be protective against enzymatic degradation. Analysis by NMR and molecular dynamics simulations indicated an interaction of Trp3 with lipid membranes, suggesting the possibility of a membrane-mediated mechanism of action for this peptide.

Stereoselective synthesis and structural elucidation of dicarba peptides.

A facile stereoselective synthesis of cis and trans unsaturated dicarba peptides has been established using preformed diaminosuberic acid derivatives as bridging units. In addition, characteristic spectral differences in the (13)C-NMR spectra of the cis- and trans-isomers show that the chemical shift of carbons in the Δ4,5-diaminosuberic acid residue can be used to assign stereochemistry in unsaturated dicarba peptides formed from ring closing metathesis of linear peptide sequences.

Structural Basis for the Inhibition of Voltage-gated Sodium Channels by Conotoxin µO§-GVIIJ.

Cone snail toxins are well known blockers of voltage-gated sodium channels, a property that is of broad interest in biology and therapeutically in treating neuropathic pain and neurological disorders. Although most conotoxin channel blockers function by direct binding to a channel and disrupting its normal ion movement, conotoxin µO§-GVIIJ channel blocking is unique, using both favorable binding interactions with the channel and a direct tether via an intermolecular disulfide bond. Disulfide exchange is possible because conotoxin µO§-GVIIJ contains anS-cysteinylated Cys-24 residue that is capable of exchanging with a free cysteine thiol on the channel surface. Here, we present the solution structure of an analog of µO§-GVIIJ (GVIIJ[C24S]) and the results of structure-activity studies with synthetic µO§-GVIIJ variants. GVIIJ[C24S] adopts an inhibitor cystine knot structure, with two antiparallel ß-strands stabilized by three disulfide bridges. The loop region linking the ß-strands (loop 4) presents residue 24 in a configuration where it could bind to the proposed free cysteine of the channel (Cys-910, rat NaV1.2 numbering; at site 8). The structure-activity study shows that three residues (Lys-12, Arg-14, and Tyr-16) located in loop 2 and spatially close to residue 24 were also important for functional activity. We propose that the interaction of µO§-GVIIJ with the channel depends on not only disulfide tethering via Cys-24 to a free cysteine at site 8 on the channel but also the participation of key residues of µO§-GVIIJ on a distinct surface of the peptide.