A histidine binding protein of Escherichia Coli: A component of cystine binding protein of Escherichia Coli

Commercially obtained cystine binding protein (CBP), an osmotic shock protein of Escherichia coli, was studied in an effort to determine its binding characteristics. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS/PAGE) analysis of commercially obtained CBP showed three protein bands. N-terminal amino acid microsequencing and subsequent computersearch revealed that the sequence of one of these proteins (25-kDa) was nearlyidentical to histidine binding protein (His J) of Salmonella typhimurium. Purification of CBP by HPLC yielded four protein peaks, of which one bound histidineexclusively. Binding was maximal at pH 5.0 to 6.0, at 4°C, did not require calciumor magnesium ions and was not inhibited by reduction of CBP disulfide bonds. Amino acids other than histidine or cystine did not bind to CBP. These data show that commercially available CBP is not a homogenous protein; it contains a histidine as well as a cystine binding component.