title: Maltose-binding protein interacts simultaneously and asymmetrically with both subunits of the Tar chemoreceptor.
abstract: The Tar chemotactic signal transducer of Escherichia coli mediates attractant responses to L-aspartate and to maltose. Aspartate binds across the subunit interface of the periplasmic receptor domain of a Tar homodimer. Maltose, in contrast, first binds to the periplasmic maltose-binding protein (MBP), which in its ligand-stabilized closed form then interacts with Tar. Intragenic complementation was used to determine the MBP-binding site on the Tar dimer. Mutations causing certain substitutions at residues Tyr-143, Asn-145, Gly-147, Tyr-149, and Phe-150 of Tar lead to severe defects in maltose chemotaxis, as do certain mutations affecting residues Arg-73, Met-76, Asp-77, and Ser-83. These two sets of mutations defined two complementation groups when the defective proteins were co-expressed at equal levels from compatible plasmids. We conclude that MBP contacts both subunits of the Tar dimer simultaneously and asymmetrically. Mutations affecting Met-75 could not be complemented, suggesting that this residue is important for association of MBP with each subunit of the Tar dimer. When the residues involved in interaction with MBP were mapped onto the crystal structure of the Tar periplasmic domain, they localized to a groove at the membrane-distal apex of the domain and also extended onto one shoulder of the apical region.
authors.affiliation: Department of Biology, Texas A&M University, College Station 77843-3258, USA.
authors.forename: P J
authors.initials: PJ
authors.lastname: Gardina
authors.forename: A F
authors.initials: AF
authors.lastname: Bormans
authors.forename: M A
authors.initials: MA
authors.lastname: Hawkins
authors.forename: J W
authors.initials: JW
authors.lastname: Meeker
authors.forename: M D
authors.initials: MD
authors.lastname: Manson
mesh_terms: D018528:ATP-Binding Cassette Transporters; D000483:Alleles; D001224:Aspartic Acid / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D002628:Chemoreceptor Cells; D002633:Chemotaxis / Q000235:genetics / Q000502:physiology; D004252:DNA Mutational Analysis; D004347:Drug Interactions; D004926:Escherichia coli / Q000235:genetics / Q000502:physiology; D029968:Escherichia coli Proteins; D015870:Gene Expression / Q000235:genetics / Q000502:physiology; D005798:Genes, Bacterial / Q000235:genetics / Q000502:physiology; D005816:Genetic Complementation Test; D008320:Maltose / Q000378:metabolism; D058619:Maltose-Binding Proteins; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D009004:Monosaccharide Transport Proteins; D033902:Periplasmic Binding Proteins; D011956:Receptors, Cell Surface / Q000235:genetics / Q000502:physiology*
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; C461619:MalE protein, E coli; D058619:Maltose-Binding Proteins; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; D033902:Periplasmic Binding Proteins; D011956:Receptors, Cell Surface; C057331:Tar protein, E coli; C461599:maltose transport system, E coli; D001224:Aspartic Acid; D008320:Maltose