title: Exploring the role of amino acid-18 of the leucine binding proteins of E. coli.
abstract: Two periplasmic binding proteins of E. coli, the leucine specific-binding protein (LS) and leucine-isoleucine-valine binding protein (LIV), have high similarity in their structure and function, but show different substrate specificity. A key difference between these proteins is residue 18 in the binding pocket, a tryptophan residue in the LS and a tyrosine residue in the LIV. To examine the role of this residue in binding specificity, we used fluorescence and (19)F NMR to monitor ligand binding to three mutants: LSW18Y, LSW18F and LIVY18W. We observed leucine binding to all proteins. LS binds L-phenylalanine but the mutation from Trp to Tyr or Phe disallows this ligand and expands the binding repertoire to L-isoleucine and L-valine. The LIVY18W mutant still retains the ability to bind L-isoleucine and also binds L-phenylalanine.
authors.affiliation: Department of Chemistry, Clarkson University, Potsdam, NY 13699, USA.
authors.forename: Branka
authors.initials: B
authors.lastname: Salopek-Sondi
authors.forename: Derrick
authors.initials: D
authors.lastname: Swartz
authors.forename: Pamela S
authors.initials: PS
authors.lastname: Adams
authors.forename: Linda A
authors.initials: LA
authors.lastname: Luck
mesh_terms: D000595:Amino Acid Sequence; D000597:Amino Acids, Branched-Chain / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D005798:Genes, Bacterial; D007930:Leucine / Q000378:metabolism*; D008024:Ligands; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D019906:Nuclear Magnetic Resonance, Biomolecular; D017354:Point Mutation; D011487:Protein Conformation; D011489:Protein Denaturation; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D014364:Tryptophan / Q000378:metabolism; D014508:Urea
chemical_list: D000597:Amino Acids, Branched-Chain; D001426:Bacterial Proteins; D008024:Ligands; D008565:Membrane Proteins; D014364:Tryptophan; D014508:Urea; D007930:Leucine