SUBSTITUTION OF THE CYSTEINYL RESIDUE (CYS21) OF SUBUNIT-B OF THE ATP SYNTHASE FROM ESCHERICHIA-COLI

Abstract

The F(o) complex of the ATP synthase (F1F(o)) of Escherichia coli contains only two cysteinyl residues, Cys21, of the two copies of subunit b. Modification of Cys21 with the hydrophobic maleimide N-(7-dimethylamino-4-methyl-coumarinyl)maleimide resulted in impairment of F(o) functions [Schneider, E. & Altendorf, K. (1985) Eur. J. Biochem. 153, 105-109]. We replaced this residue (via cassette mutagenesis) by Ser, Gly, Ala, Thr, Asp and Pro. None of the replacements resulted in detectable alterations of the function of the ATP synthase, making a functional role for these sulfhydryl residues unlikely. Due to its high tolerance towards amino acid substitutions, the region around Cys21 seems not to be a protein-protein contact area.