Substrate binding causes movement in the ATP binding domain of Escherichia coli adenylate kinase

Crystallographic evidence suggests that there is a large hinged domain motion associated with substrate binding in adenylate kinase. To test this hypothesis, resonance energy transfer measurements of substrate binding were initiated. Adenylate kinase from Escherichia coli consists of three domains: the main body of the enzyme with alpha-helical and beta-sheet secondary structure, and domains that close over the AMP and ATP binding sites. Four single tryptophan mutants were constructed to map distances. Two tryptophan mutants were positioned at residues 133 (Y133W) and 137 (F137W), which are in the domain that closes over the ATP binding site. Mutant F86W that is located at the AMP binding site, and mutant S41W that is in the loop that close over AMP, complete the mapping library. Energy transfer was measured between each of these tryptophans and 5-[[2-(acetylamino)ethyl]amino]naphthalene-1-sulfonic acid (AEDANS) covalently bound to the single cysteine residue at position 77, which is located in the main body of adenylate kinase. The distance between the tryptophan of the F137W mutant adenylate kinase and the AEDANS-labeled Cys-77 decreased by 12.1 A upon the binding of the bisubstrate inhibitor P1, P5-bis(5'-adenosyl) pentaphosphate (AP5A). There were only small alterations in the tryptophan to Cys-77-AEDANS distances in the Y133W, F86W, and S41W mutants upon the binding of AP5A, ATP, or AMP, implying that movement of residues 133, 86, and 41 in relation to the Cys-77 residue was minimal. These results suggest that there is significant closure of the ATP binding domain upon the binding of ATP or AP5A. Unexpectedly, exposure of the enzyme to AMP also introduced a partial closure of the ATP hinged domain.