Research 1 | Beckstein Lab

G protein-coupled receptors (GPCRs) make up the largest family of proteins in mammalian cells. These receptors are known to be sensitive to cholesterol in the cellular membrane. Coarse-grained molecular dynamics (CGMD) was used to identify specific protein-cholesterol interaction sites. The analysis showed differential cholesterol binding on equivalent residues in homologues known to have different sensitivities to cholesterol.

NHE9 is a sodium/proton exchanger in mammals, part of a large family of secondary active transporters. Our collaborators (David Drew at the University of Stockholm) solved the structure of NHE9 (SLC9A9) from horse with cryo electron-microscopy to 3.2 Å resolution in an inward facing conformation, the first structure of a mammalian sodium/proton antiporter. Functional measurements, structural bioinformatics, and MD simulations all indicate that many components of the transport mechanism are similar between prokaryotic and mammalian sodium/proton antiporters.

Transport of ions and small molecules across the cell membrane against electrochemical gradients is catalyzed by integral membrane proteins that use a source of free energy to drive the energetically uphill flux of the transported substrate. Here we review general principles that apply to most secondary active transporters, namely energy coupling through kinetic cycles and the thermodynamic driving forces, inverted repeat symmetry as a means to generate bi-stable systems that can function according to the alternating access model, and understanding transporters as gated pores.