title: The lipid bilayer determines helical tilt angle and function in lactose permease of Escherichia coli.
abstract: The structure of lactose permease from Escherichia coli in its lipid environment was studied by attenuated total reflection Fourier transform infrared spectroscopy. The protein exhibits an alpha-helical content of about 65% and about 25% beta-sheet. Unusually fast hydrogen/deuterium (H/D) exchange to 90-95% completion suggests a structure that is highly accessible to the aqueous phase. An average tilt angle of 33 degrees for the helices was found with respect to the bilayer normal at a lipid-to-protein ratio of approximately 800:1 (mol/mol), and the permease exhibits optimal activity under these conditions. However, upon decreasing the lipid-to-protein ratio, activity decreases continuously in a manner that correlates with the decrease in the lipid order parameter and the increase in the average helical tilt angle. Taken together, the data indicate that the structure and function of the permease are strongly dependent on the order and integrity of the lipid bilayer.
authors.affiliation: Howard Hughes Medical Institute, Department of Physiology, Molecular Biology Institute, University of California, Los Angeles, CA 90095-1662, USA.
authors.forename: J
authors.initials: J
authors.lastname: le Coutre
authors.forename: L R
authors.initials: LR
authors.lastname: Narasimhan
authors.forename: C K
authors.initials: CK
authors.lastname: Patel
authors.forename: H R
authors.initials: HR
authors.lastname: Kaback
mesh_terms: D017666:Deuterium Oxide / Q000737:chemistry; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D008051:Lipid Bilayers; D026901:Membrane Transport Proteins / Q000737:chemistry*; D009004:Monosaccharide Transport Proteins; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared; D027981:Symporters
chemical_list: D029968:Escherichia coli Proteins; C050221:LacY protein, E coli; D008051:Lipid Bilayers; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D027981:Symporters; C021499:lactose permease; D017666:Deuterium Oxide