The lactose permease of Escherichia coli: overall structure, the sugar-binding site and the alternating access model for transport.
Membrane transport proteins transduce free energy stored in electrochemical ion gradients into a concentration gradient and are a major class of membrane proteins, many of which play important roles in human health and disease. Recently, the X-ray structure of the Escherichia coli lactose permease (LacY), an intensively studied member of a large group of related membrane transport proteins, was solved at 3.5 A. LacY is composed of N- and C-terminal domains, each with six transmembrane helices, symmetrically positioned within the molecule. The structure represents the inward-facing conformation, as evidenced by a large internal hydrophilic cavity open to the cytoplasmic side. The structure with a bound lactose homolog reveals the sugar-binding site in the cavity, and a mechanism for translocation across the membrane is proposed in which the sugar-binding site has alternating accessibility to either side of the membrane.
Abramson
Jeff
J
Department of Biological Sciences, Imperial College London, London SW7 2AZ, UK.
Smirnova
Irina
I
Kasho
Vladimir
V
Verner
Gillian
G
Iwata
So
S
Kaback
H Ronald
HR
D001665:Binding Sites; D001693:Biological Transport, Active; D050260:Carbohydrate Metabolism; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D009004:Monosaccharide Transport Proteins; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D055672:Static Electricity; D027981:Symporters; D013816:Thermodynamics
D029968:Escherichia coli Proteins; C050221:LacY protein, E coli; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D027981:Symporters; C021499:lactose permease