Amino acid residues involved in the functional integrity of Escherichia coli methionine aminopeptidase

Amino acid residues in the metal-binding and putative substrate-binding sit es of Escherichia coli methionine aminopeptidase (MAP) were mutated, and th eir effects on the function of the enzyme were investigated, Substitution o f any amino acid residue at the metal-binding site resulted in complete los s of the two cobalt ions bound to the protein and diminished the enzyme act ivity. However, only Cys70 and Trp221 at the putative substrate-binding sit e are involved in the catalytic activity of MAP. Changing either of them ca used partial loss of enzyme activity, while mutations at both positions abo lished MAP function. Both residues are found to be conserved in type I but not type II MAPs.