On the binding of ATP to the autophosphorylating protein, Ptk, of the bacterium Acinetobacter johnsonii

The autophosphorylating protein, Ptk, of the bacterium Acinetobacter johnso nii was overproduced, purified to homogeneity and assayed for ATP binding b y using the nucleotide analog 5'-p-fluorosulfonylbenzoyl adenosine, The ATP binding site of this bacterial autophosphorylating protein was found to be different from that generally used by eukaryotic protein kinases, It consi sts of two amino acid sequences that closely resemble the Walker motifs A a nd B, This observation was confirmed by site-directed mutagenesis experimen ts which showed, in addition, that the ATP molecule bound to these motifs i s effectively employed by the bacterial protein to autophosphorylate on tyr osine, It is concluded that even though the overall autophosphorylation rea ction is similar in eukaryotic and prokaryotic proteins, the mechanism invo lved is likely different. (C) 1999 Federation of European Biochemical Socie ties.