The chemical design or redesign of proteins with significant biological activity presents formidable challenges. Ion channels offer advantages for such design studies because one can examine the function of single molecular entities in real time. Gramicidin channels are attractive for study because of their known structure and exceptionally well-defined function. This article focuses on amino acid sequence changes that redesign the structure or function of gramicidin channels. New, and functional, folded states have been achieved. In some cases, a single amino acid sequence can give rise to several (up to three) functional conformations. Single amino acid substitutions confer voltage-dependent channel gating. The findings provide insight into the folding of integral membrane proteins, the importance of tryptophan residues at the membrane/water interface, and the mechanism of channel gating.

Bacterial pathogens like Mycobacterium tuberculosis (Mtb) encounter acidic microenvironments in the host and must maintain their acid-base homeostasis to survive. A genetic screen identified two Mtb strains that cannot control intrabacterial pH (pHIB) in an acidic environment; infection with either strain led to severe attenuation in mice. To search for additional proteins that Mtb requires to survive at low pH, we introduced a whole-cell screen for compounds that disrupt pHIB, along with counter-screens that identify ionophores and membrane perturbors. Application of these methods to a natural product library identified four compounds of interest, one of which may inhibit novel pathway(s). This approach yields compounds that may lead to the identification of pathways that allow Mtb to survive in acidic environments, a setting in which Mtb is resistant to most of the drugs currently used to treat tuberculosis.

In a retrospective study of patients who had undergone myringoplasty at our department within a 12-month period, we assessed the graft take rate using tri-adcortyl ointment (TAO) as ear dressing. Data including age, site and size of perforation, grade of surgeon, surgical approach, use of postoperative ear dressings, complications and audiometric outcome was collected from the patient notes and analysed. The overall success rate of the operation (with success being defined as an intact tympanic membrane at 6 months) was noted. Seventy-seven patients were operated, but data were complete on 64 patients and these constituted the study population. TAO was used in 95% of the patients and BIPP gauze pack in the remaining 5%. Age ranged from 8 to 63 years (mean 34 years). Mean follow-up period was 13 months. Most of the operations (72.88%) were carried out by consultants with a success rate of 89% and the remaining patients were operated by trainees with a success rate of 88% (P = 1.000). The overall success rate was 89, 90.16% for TAO and 66.66% (2 out of 3) for BIPP (P = 0.298), 95% for small and 86% for subtotal perforations (P = 0.573), 85% for anterior and 100% for posterior perforations (P = 0.240), 91% for adult patients and 88% for children (P = 1.000). TAO is a suitable ear dressing in myringoplasty. Routine use of TAO did not affect the success rate of myringoplasty at our centre.

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and mediates blood coagulation, bone development and viral infection. Despite the recent advances in understanding the structure-function of the fungal TMEM16-CaPLSases, how mammalian CaPLSases open and close, or gate their phospholipid permeation pathways remains unclear. Through functional and computational approaches, here we identified TMEM16F-CaPLSase's inner activation gate. Disrupting the inner gate residues dramatically altered TMEM16F phospholipid permeation. Interestingly, a gain-of-function mutation at the inner activation gate not only made TMEM16F CaPLSase constitutively open, but also converted TMEM16A Ca 2þ -activated Clchannel (CaCC) to a CaPLSase. A gating model is proposed to describe the Ca 2þ -dependent gating mechanism of TMEM16 CaPLSases. 133-PlatPrediction of the Closed Conformation and Insights into the Mechanism of the Membrane Enzyme LpxR . Covalent modification of outer membrane lipids of Gram-negative bacteria can impact the ability of the bacterium to develop resistance to antibiotics as well as modulating the immune response of the host. The enzyme LpxR from Salmonella typhimurium is known to deacylate lipopolysaccharide molecules of the outer membrane, however the mechanism of action is unknown. Here we employ molecular dynamics and Monte Carlo simulations to study the conformational dynamics and substrate binding of LpxR in representative outer membrane models and also detergent micelles. We examine the roles of conserved residues and provide an understanding of how LpxR binds its substrate. Our simulations predict that the catalytic H122 must be N 3-protonated for a single water molecule to occupy the space between it and the scissile bond, with a free binding energy of À8.5 kcal mol À1 . Furthermore, simulations of the protein within a micelle enable us to predict the structure of the putative 'closed' protein. Our results highlight the need for including dynamics, a representative environment and the consideration of multiple tautomeric and rotameric states of key residues in mechanistic studies; static structures alone do not tell the full story. 134-PlatStudying Conformation of the Voltage-Sensor Domain (VSD) of the Human KCNQ1 Potassium Ion Channel in Proteoliposomes using EPR KCNQ1 is a voltage-gated potassium channel modulated by members of the KCNE protein family. KCNQ1 is involved in the cardiac repolarization phase of the heart beat and K þ homeostasis in the inner ear. Dysfunction of KCNQ1 causes several diseases including several cardiac arrhythmias, congenital deafness, and type II diabetes mellitus. Human KCNQ1 is a 676-residue protein consisting of 100-residue N-terminal cytosolic domain, followed by an $260-residue channel domain containing six transmembrane (TMD) helices, and a 300-residue cytosolic C-terminus. The first four TMD helices (S1-S4) form the voltage-sensor domain (Q1-VSD) that is linked to the pore domain (helices S5 and S6). Roughly 40% of the >200 reported disease-related mutations in the KCNQ1 gene result in amino acid substitutions in the VSD, mak...

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SS‐31 is a mitochondria‐targeted therapeutic, currently in Phase 2 clinical trials, which protects cristae structure, prevents swelling of mitochondria and improves cellular respiration. We previously identified the target of SS‐31 as cardiolipin (CL), a phospholipid found only in the inner mitochondrial membrane. Here we utilize DOSY NMR to show that the diffusion rate of SS‐31 is reduced in the presence of CL‐containing bicelles, which is the first kinetic information on the interaction of SS‐31 with CL‐containing membranes. Because mitochondrial swelling involves solute transfer across the membrane, in addition to the changes in membrane morphology, it became important to test for membrane‐perturbing effects of SS‐31, particularly In light of evidence that membrane‐perturbation predicts toxicity for small molecules. We utilize a gramicidin‐based fluorescence assay using CL‐containing liposomes to assess drug‐induced membrane perturbations. We find that SS‐31 has no effect on synthetic membrane systems, even at several log orders above therapeutic concentration. The lack of membrane effects suggest that SS‐31 has no toxicity on the membrane, which is consistent with safety data from Phase 1 trials.