Lactose permease H+-lactose symporter: mechanical switch or Brownian ratchet?

ABSTRACT: Lactose permease structure is deemed consistent with a mechanical switch device for H(+)-coupled symport. Because the crystallography-assigned docking position of thiodigalactoside (TDG) does not make close contact with several amino acids essential for symport; the switch model requires allosteric interactions between the proton and sugar binding sites. The docking program, Autodock 3 reveals other lactose-docking sites. An alternative cotransport mechanism is proposed where His-322 imidazolium, positioned in the central pore equidistant (5-7 A) between six charged amino acids, Arg-302 and Lys-319 opposing Glu-269, Glu-325, Asp-237, and Asp-240, transfers a proton transiently to an H-bonded lactose hydroxyl group. Protonated lactose and its dissociation product H(3)O+ are repelled by repr

SUBMITTER: Naftalin RJ 

PROVIDER: S-EPMC1853157 | biostudies-literature | 2007 May

REPOSITORIES: biostudies-literature