Inferences about the catalytic domain of P-type ATPases from the tertiary structures of enzymes that catalyze the same elementary reaction.

The machinery to catalyze elementary reactions is conserved, and the number of solved enzyme structures is increasing exponentially. Therefore, structures of enzymes that catalyze phosphate transfer are reviewed, and a supersecondary structure connecting the Walker A sequence to another sequence containing functional amino acids is proposed as an additional signature for the active site. The new signature is used to infer the identity of the P-loop in P-type biological pumps and may be useful in predicting targets for site-directed mutagenesis in other enzymes of unknown structure like the AAA family and ABC transporters.