Lactose permease

From Wikipedia, the free encyclopedia
Jump to: navigation, search
LacY proton/sugar symporter
Crystal Structure of Lactose Permease in Complex with an Affinity Inactivator. PDB 2y5y[1]
Symbol LacY_symp
Pfam PF01306
Pfam clan CL0015
InterPro IPR022814
TCDB 2.A.1
OPM superfamily 15
OPM protein 2cfq

Lactose permease is a membrane protein which is a member of the major facilitator superfamily. Lactose permease can be classified as a symporter, which uses the proton gradient towards the cell to transport β-galactosides such as lactose in the same direction into the cell.

The protein has twelve transmembrane alpha-helices and its molecular weight is 45,000 Daltons.[2] It exhibits an internal two-fold symmetry, relating the N-terminal six helices onto the C-terminal helices. It is encoded by the lacY gene in the lac operon.

The sugar lies in the hydrophilic core of the protein which is accessible from the periplasm.[2] On binding, a large conformational change takes place which makes the sugar binding site accessible from the cytoplasm.

Mechanism: hydrogen from the outside of the cell binds to a carboxyl group on the enzyme that allows it to undergo a conformational change. This form of lactose permease can bind lactose from outside the cell. The enzyme then everts and lactose is transported inward.

The X-ray crystal structure was first solved in 2003 by J. Abramson et al. [3]


  1. ^ Chaptal, V.; Kwon, S.; Sawaya, M. R.; Guan, L.; Kaback, H. R.; Abramson, J. (2011). "Crystal structure of lactose permease in complex with an affinity inactivator yields unique insight into sugar recognition". Proceedings of the National Academy of Sciences. 108 (23): 9361–9366. doi:10.1073/pnas.1105687108. PMC 3111295Freely accessible. PMID 21593407. 
  2. ^ a b Hammes, Gordon G. (2005). Spectroscopy for the biological sciences. Hoboken, N.J.: Wiley-Interscience. p. 140. ISBN 9780471713449. 
  3. ^ Abramson, J.; Smirnova, I.; Kasho, V.; Verner, G.; Kaback, H. R.; Iwata, S. (2003). "Structure and Mechanism of the Lactose Permease of Escherichia coli". Science. 301 (5633): 610–615. doi:10.1126/science.1088196. PMID 12893935.