Yamato I, Anraku Y
Department of Biology, Faculty of Science, University of Tokyo, Japan.
J Biol Chem. 1988 Nov 5;263(31):16055-7.
Cys-281, Cys-344, or Cys-349 in the proline carrier of Escherichia coli was changed to a serine residue by site-specific mutagenesis. The activities of the resultant mutants for uptake of proline were as great as that of the wild-type strain. These mutant carriers were all as sensitive as the wild-type carrier to the proline analogue azetidine 2-carboxylate. However, the mutant carriers with Ser-281 and Ser-344 were resistant to N-ethylmaleimide, whereas the mutant carrier with Ser-349 was as sensitive as the wild-type carrier to this reagent. These results indicate that these cysteine residues are not essential for proline transport and that Cys-281 and Cys-344 may be close to the substrate-binding site that contains an N-ethylmaleimide-sensitive residue.
通过定点诱变将大肠杆菌脯氨酸载体中的半胱氨酸-281、半胱氨酸-344或半胱氨酸-349改变为丝氨酸残基。所得突变体摄取脯氨酸的活性与野生型菌株一样高。这些突变载体对脯氨酸类似物氮杂环丁烷-2-羧酸的敏感性均与野生型载体相同。然而，含有丝氨酸-281和丝氨酸-344的突变载体对N-乙基马来酰亚胺具有抗性，而含有丝氨酸-349的突变载体对该试剂的敏感性与野生型载体相同。这些结果表明，这些半胱氨酸残基对于脯氨酸转运并非必不可少，并且半胱氨酸-281和半胱氨酸-344可能靠近含有对N-乙基马来酰亚胺敏感残基的底物结合位点。
