title: Chaperonin-promoted post-translational membrane insertion of a multispanning membrane protein lactose permease.
abstract: Using an in vitro membrane-free translation system from Escherichia coli, it is shown that chaperonin GroEL added cotranslationally interacts with newly synthesized lactose permease (LacY), a polytopic membrane protein, thereby preventing aggregation. Subsequently, when the isolated GroEL-LacY complex is incubated with inverted membrane vesicles, the permease is inserted into the membrane in a MgATP-dependent manner. Post-translational membrane insertion is also observed when aggregation of newly synthesized LacY is prevented by addition of the nonionic detergent n-dodecyl-beta,D-maltoside during translation in place of GroEL. No membrane integration occurs with right-side-out vesicles, indicating that LacY interacts specifically only with the cytosolic face of the membrane. Ligand thiodigalactoside protection against alkylation of the Cys-148 residue in the permease shows proper post-translational insertion. Moreover, limited proteolysis of soluble LacY either complexed with GroEL or in detergent indicates that the newly synthesized protein assumes a conformation that is comparable to that of native, membrane-embedded permease prior to insertion into the membrane.
authors.affiliation: Department of Biochemistry, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: E
authors.initials: E
authors.lastname: Bochkareva
authors.forename: A
authors.initials: A
authors.lastname: Seluanov
authors.forename: E
authors.initials: E
authors.lastname: Bibi
authors.forename: A
authors.initials: A
authors.lastname: Girshovich
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001692:Biological Transport; D018834:Chaperonin 60 / Q000378:metabolism*; D003545:Cysteine / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins; D011499:Protein Processing, Post-Translational; D027981:Symporters
chemical_list: D018834:Chaperonin 60; D029968:Escherichia coli Proteins; C050221:LacY protein, E coli; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D027981:Symporters; D000255:Adenosine Triphosphate; C021499:lactose permease; D003545:Cysteine