Allosteric rescue of catalytically impaired ATP phosphoribosyltransferase variants links protein dynamics to active-site electrostatic preorganisation

Abstract

ATP phosphoribosyltransferase, which catalyzes the first step of histidine biosynthesis, is regulated by a complex allosteric mechanism involving the regulatory protein HisZ and the catalytic subunit HisGS. HisZ enhances catalysis and mediates inhibition by histidine, even though it binds about 20 Å away from the active site.</p><p>The study shows that mutations in key active-site residues of HisGS that impair catalysis can be functionally rescued by HisZ. Molecular dynamics simulations reveal that HisZ binding restricts HisGS dynamics, promoting a preorganized active site in which Arg56 and Arg32 stabilize the departure of the pyrophosphate leaving group. In the Arg56Ala mutant, HisZ shifts Arg32 dynamics to partially compensate for the missing Arg56.</p><p>Overall, the work demonstrates how long-range protein–protein interactions can restore catalytic activity by reestablishing electrostatic preorganization at the active site, highlighting a mechanism for allosteric rescue and catalytic resilience.