H+/Lactose Membrane Transport Protein, LacY
Living reference work entry
LacY ( aka Lac permease) is the product of the lacY gene, the second structural gene in the lac operon, which encodes a single polypeptide that is solely responsible for all the translocation reactions of β-galactoside transport in E. coli. LacY (TCDB 2.A.1.5.1) belongs to the oligosaccharide/H + symporter subfamily of the major facilitator superfamily (MFS). LacY is selective for disaccharides containing a d-galactopyranosyl ring, as well as d-galactose, with no affinity for d-glucopyranosides or d-glucose. The native substrate is lactose, which is a disaccharide derived from the condensation of galactose and glucose at a β-1 → 4 glycosidic linkage. The systematic name is β-d-galactopyranosyl-(1 → 4)-d-glucose (Fig. 1). LacY catalyzes reversible translocations of one cargo sugar with one proton (H +), and the coupled translocation between H +and the sugar in the same direction is obligatory. The reaction can be described by the...
© European Biophysical Societies' Association (EBSA) 2018