Neighboring group participation in the transition state of human purine nucleoside phosphorylase.

ABSTRACT: The X-ray crystal structures of human purine nucleoside phosphorylase (PNP) with bound inosine or transition-state analogues show His257 within hydrogen bonding distance of the 5'-hydroxyl. The mutants His257Phe, His257Gly, and His257Asp exhibited greatly decreased affinity for Immucillin-H (ImmH), binding this mimic of an early transition state as much as 370-fold (Km/Ki) less tightly than native PNP. In contrast, these mutants bound DADMe-ImmH, a mimic of a late transition state, nearly as well as the native enzyme. These results indicate that His257 serves an important role in the early stages of transition-state formation. Whereas mutation of His257 resulted in little variation in the PNP x DADMe-ImmH x SO4 structures, His257Phe x ImmH x PO4 showed distortion at the 5'-hydroxyl, indica

SUBMITTER: Murkin AS 

PROVIDER: S-EPMC2526054 | biostudies-literature | 2007 May

REPOSITORIES: biostudies-literature