title: The interaction between aspartic acid 237 and lysine 358 in the lactose carrier of Escherichia coli.
abstract: The lacY from Escherichia coli strains 020 and AE43 have been cloned on plasmids which were designated p020-K358T and pAE43-D237N. These lacY mutants contain amino acid substitutions changing Lys-358 to Thr or Asp-237 to Asn, respectively. The charge neutralizing effect of each mutation is associated with a functional defect in melibiose transport which we exploited in order to isolate second site revertants to the melibiose-positive phenotype. Eleven melibiose-positive revertants of p020-K358T were isolated. All contained a second-site mutation converting Asp-237 to a neutral amino acid (8 to Asn, 1 to Gly, and 2 to Tyr). Twelve melibiose-positive revertants of pAE43-D237N were isolated. Two were second-site revertants converting Lys-358 to a neutrally Gln residue, while the remainder directly reverted Asn-237 to the wild-type Asp-237. We conclude that the functional intimate relationship between Asp-237 and Lys-358 suggests that these residues may be closely juxtaposed in three-dimensional space, possibly forming a 'charge-neutralizing' salt bridge.
authors.affiliation: Department of Cellular and Molecular Physiology, Harvard Medical School, Boston, MA 02115.
authors.forename: S C
authors.initials: SC
authors.lastname: King
authors.forename: C L
authors.initials: CL
authors.lastname: Hansen
authors.forename: T H
authors.initials: TH
authors.lastname: Wilson
mesh_terms: D000595:Amino Acid Sequence; D001224:Aspartic Acid / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001692:Biological Transport / Q000502:physiology; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D007785:Lactose / Q000378:metabolism; D008239:Lysine / Q000737:chemistry; D008553:Melibiose / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008756:Methylgalactosides / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins; D016297:Mutagenesis, Site-Directed; D011522:Protons; D027981:Symporters; D013862:Thiogalactosides / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C050221:LacY protein, E coli; D026901:Membrane Transport Proteins; D008756:Methylgalactosides; D009004:Monosaccharide Transport Proteins; D011522:Protons; D027981:Symporters; D013862:Thiogalactosides; C009468:thiomethylgalactoside; D001224:Aspartic Acid; C021499:lactose permease; D008553:Melibiose; D007785:Lactose; D008239:Lysine