Overlap between folding and functional energy landscapes for adenylate kinase conformational change.

Enzyme function is often dependent on fluctuations between inactive and active structural ensembles. Adenylate kinase isolated from Escherichia coli (AK(e)) is a small phosphotransfer enzyme in which interconversion between inactive (open) and active (closed) conformations is rate limiting for catalysis. AK(e) has a modular three-dimensional architecture with two flexible substrate-binding domains that interact with the substrates AMP, ADP and ATP. Here, we show by using a combination of biophysical and mutagenic approaches that the interconversion between open and closed states of the ATP-binding subdomain involves partial subdomain unfolding/refolding in an otherwise folded enzyme. These results provide a novel and, possibly general, molecular mechanism for the switch between open and closed conformations in AK(e).