title: Site-directed mutagenesis of the alpha subunit of tryptophan synthase from Salmonella typhimurium.
abstract: Site-specific mutagenesis has been used to prepare two mutant forms of the alpha subunit of tryptophan synthase from Salmonella typhimurium in which either cysteine-81 or cysteine-118 is replaced by a serine residue. These mutant proteins are potentially useful for x-ray crystallographic studies since a heavy metal binding site is specifically eliminated in each mutant. The purified mutant proteins are fully active in four reactions catalyzed by the wild type alpha 2 beta 2 complex of tryptophan synthase. However, the mutant alpha 2 beta 2 complexes dissociate more readily and are less heat-stable than the wild type alpha 2 beta 2 complex. Thus, cysteine-81 and cysteine-118 of the alpha subunit serve structural but not functional roles.
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D003553:Cystine; D004926:Escherichia coli / Q000235:genetics; D046911:Macromolecular Substances; D009154:Mutation; D010957:Plasmids; D012486:Salmonella typhimurium / Q000201:enzymology / Q000235:genetics*; D012694:Serine; D014367:Tryptophan Synthase / Q000235:genetics* / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D046911:Macromolecular Substances; D012694:Serine; D003553:Cystine; D014367:Tryptophan Synthase