Perceived exertion is not a substitute for fatiguability in spinal muscular atrophy.

Introduction/aims: Fatiguability and perceived fatigue are common unrelated symptoms in ambulatory individuals with spinal muscular atrophy (SMA). Ratings of perceived exertion (RPE) measures the sense of effort during an activity and has been used as a proxy for fatigue. Relationships between perceived fatigue, fatiguability, and RPE have been described in healthy populations, but the relationship in SMA has not been examined.

Expanding the membrane-protein NMR toolkit.

An NMR method to monitor conformational states of challenging large protein targets is described. The method, which can be used to evaluate distances between two labels and to measure conformational exchange rates, revealed an unanticipated outward-facing state in a glutamate transporter.

A CLC-ec1 mutant reveals global conformational change and suggests a unifying mechanism for the CLC Cl/H transport cycle.

Among coupled exchangers, CLCs uniquely catalyze the exchange of oppositely charged ions (Cl for H). Transport-cycle models to describe and explain this unusual mechanism have been proposed based on known CLC structures. While the proposed models harmonize with many experimental findings, gaps and inconsistencies in our understanding have remained.

Revealing an outward-facing open conformational state in a CLC Cl(-)/H(+) exchange transporter.

CLC secondary active transporters exchange Cl(-) for H(+). Crystal structures have suggested that the conformational change from occluded to outward-facing states is unusually simple, involving only the rotation of a conserved glutamate (Gluex) upon its protonation. Using (19)F NMR, we show that as [H(+)] is increased to protonate Gluex and enrich the outward-facing state, a residue ~20 Å away from Gluex, near the subunit interface, moves from buried to solvent-exposed.

13C NMR detects conformational change in the 100-kD membrane transporter ClC-ec1.

CLC transporters catalyze the exchange of Cl(-) for H(+) across cellular membranes. To do so, they must couple Cl(-) and H(+) binding and unbinding to protein conformational change. However, the sole conformational changes distinguished crystallographically are small movements of a glutamate side chain that locally gates the ion-transport pathways.

Structural modeling of calcium binding in the selectivity filter of the L-type calcium channel.

Calcium channels play crucial physiological roles. In the absence of high-resolution structures of the channels, the mechanism of ion permeation is unknown. Here we used a method proposed in an accompanying paper (Cheng and Zhorov in Eur Biophys J, 2009) to predict possible chelation patterns of calcium ions in a structural model of the L-type calcium channel.

Docking of calcium ions in proteins with flexible side chains and deformable backbones.

A method of docking Ca(2+) ions in proteins with flexible side chains and deformable backbones is proposed. The energy was calculated with the AMBER force field, implicit solvent, and solvent exposure-dependent and distance-dependent dielectric function. Starting structures were generated with Ca(2+) coordinates and side-chain torsions sampled in 1000 A(3) cubes centered at the experimental Ca(2+) positions.

Structural model for phenylalkylamine binding to L-type calcium channels.

Phenylalkylamines (PAAs), a major class of L-type calcium channel (LTCC) blockers, have two aromatic rings connected by a flexible chain with a nitrile substituent. Structural aspects of ligand-channel interactions remain unclear. We have built a KvAP-based model of LTCC and used Monte Carlo energy minimizations to dock devapamil, verapamil, gallopamil, and other PAAs.