Biophysical Society Bulletin | September 2019

Communities & Outreach

Subgroups Membrane Transport

Figure 1. Molecular simulations from the Grosman lab of pen- tameric ligand-gated ion channels (pLGICs) revealed the confor- mation of charged side chains in the selectivity filter matters for charge-sign discrimination. A common challenge for membrane proteins is interpreting pairwise distance distributions obtained from spectroscopic data in the context of known structures. Members of the Forrest lab carried out a molecular dynamics simulation study using a recently developedmaximum-entropy method called ensem- ble-biasedmetadynamics or EBMetaD (Pubmed: 26083917), which allows ranking of different crystal structures in terms of the likelihood that they reflect the conformation in the spectroscopic experiment. EBMetaD simulations of the sodium-coupled betaine transporter BetP with double-electron electron resonance data suggest, for example, that the binding site is exposed to the cyto- plasm in the presence of sodium (Pubmed: 30728216).

The Membrane Transport Subgroup saw a healthy increase of members in the last year. This increase is palpable—we had a significantly larger audience during the annual symposium and the business meeting afterward. The subgroup has 213 regular members, 60 postdoctoral members, 138 student members, and 9 emeritus members. Many thanks to all of you who signed up. Starting in 2020, all subgroups will have a half-day symposiumon Saturday during the Annual Meeting. The Ion Channels, Recep- tors and Transporters Subgroup (formerly Molecular Biophysics) will hold its symposium in the morning of February 15, 2020; we will hold our symposium in the afternoon. The two subgroups will then alternate between the morning and afternoon slots in subsequent years. Although a morning symposiumwouldmean traveling on a Friday, we hope that this arrangement will help increase participation in both symposia. We would like to use the BPS Bulletin as a platform to highlight works by our subgroupmembers, and we eagerly await sug- gestions from the subgroup. In this issue, we highlight recent publications by Claudio Grosman fromUniversity of Illinois at Urba- na-Champaign (Fig. 1), Lucy Forrest fromNIH/NINDS (Fig. 2), and Steve Long fromSloan Kettering Institute (Fig. 3). Molecular simulations from the Grosman lab revealed that, in pentameric ligand-gated ion channels (pLGICs), the conformation of charged side chains in the selectivity filter matters for charge- sign discrimination. Using structural models of anion-selective pLGICs, the authors found that, whereas some rotamers of the buried arginines at position 0’ confer high selectivity for anions, others support the permeation of cations and anions at similar rates or even allow the faster permeation of cations. Further- more, they found that modeling glutamates at position –1’––in- stead of the five native alanines––switches charge selectivity also in a conformation-dependent manner, with some glutamate rotamers being muchmore effective at conferring selectivity for cations than others.

Figure 2. Ensemble-biasedmetadynamics simulations from the Forrest lab allow ranking of different crystal structures according to the likelihood that they reflect the conformation in the spectro- scopic experiment, illustrated here for the sodium-coupled betain transporter, BetP. — Susan Rempe , Chair; Ming Zhou , Vice Chair; Lucie Delemotte , Secretary/Treasurer Numbers By the The BPS Find a Biophysicist (FaB) Network started in April 2018 and currently has 1,312 members. Connect with BPS

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