Characterizing Active Site Conformational Heterogeneity along the Trajectory of an Enzymatic Phosphoryl Transfer Reaction

States along the phosphoryl transfer reaction catalyzed by the nucleoside monophosphate kinase UmpK were captured and changes in the conformational heterogeneity of conserved active site arginine side‐chains were quantified by NMR spin‐relaxation methods. In addition to apo and ligand‐bound UmpK, a transition state analog (TSA) complex was utilized to evaluate the extent to which active site conformational entropy contributes to the transition state free energy. The catalytically essential arginine side‐chain guanidino groups were found to be remarkably rigid in the TSA complex, indicating that the enzyme has evolved to restrict the conformational freedom along its reaction path over the energy landscape, which in turn allows the phosphoryl transfer to occur selectively by avoiding side reactions. Die konformative Heterogenität von Arginin‐Seitenketten wurde entlang der durch die Nukleosidmonophosphatkinase UmpK katalysierten Phosphoryltransferreaktion quantifiziert. Die katalytisch notwendigen Gruppen sind bemerkenswert starr in einem übergangszustandsanalogen Komplex, was darauf hinweist, dass das Enzym seine konformative Freiheit entlang seines Reaktionspfades einschränkt, um so Nebenreaktionen zu vermeiden und einen selektiven Phosphoryltransfer zu ermöglichen.