Molecular Basis of Alternating Access Membrane Transport by the Sodium-hydantoin Transporter Mhp1

Abstract

Transporters are suggested to transport the substrates across the membrane using the alternating access mechanism in which the proteins have three functionally distinct conformational states, outward-facing, occluded and inward-facing. The structures from a secondary active transporter Mhp1 were recently determined in three states of the alternating access mechanism. Comparison of the structures shows that the conformational changes between these states are achieved by the rigid body movement of the four helices relative to the rest of the protein. The molecular basis of the alternating access mechanism is likely to be common among the LeuT superfamily.