Transmembrane transporters: An open and closed case

摘要

In a recent issue of PNAS, the landmark paper by Kaback et al. (1) addresses the dynamic mechanism of a transmembrane transporter of the Major Facilitator Superfamily (MFS), LacY. LacY, also called "lactose permease," harnesses the energy developed across the bacterial cell membrane as an H~+ electrochemical gradient, to take up a galactopyranoside such as lactose effectively under physiological conditions. It couples stoichiometric 1:1 translocation of one "cargo" molecule and one H~+. Thus, energetically downhill movement of H~+ drives lactose in the same direction across the membrane to concentrate the nutrient inside the cell, as in the chemiosmotic hypothesis of Mitchell and Moyle.