A single amino acid substitution in a histidine-transport protein drastically alters its mobility in sodium dodecyl sulfate-polyacrylamide gel electrophoresis

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Abstract
Mutation hisJ5625 altered the histidine-binding protein J of Salmonella typhimurium such that histidine transport is impaired, even though binding of histidine by the J protein is unimpaired. Protein analytical methods showed that the only effect of this mutation was the substitution of a cysteine residue for an arginine at a site in the interior of the polypeptide chain. This arginine residue is therefore potentially essential for the transport function of the protein. The mutant protein migrates in sodium dodecyl sulfate-polyacrylamide gel electrophoresis more slowly than the wild type protein, as if its MW were greater by as much as 2000. Since this behavior is apparently due to a single amino acid replacement, a MW difference even between 2 closely related proteins should not be inferred solely on the basis of sodium dodecyl sulfate gel electrophoresis.