New determinants in the catalytic mechanism of nucleoside hydrolases from the structures of two isozymes from Sulfolobus solfataricus

Claudia Minici, Giovanna Cacciapuoti, Ester De Leo, Marina Porcelli, Massimo Degano

Research output: Contribution to journalArticlepeer-review

Abstract

The purine- and pyrimidine-specific nucleoside hydrolases (NHs) from the archaeon Sulfolobus solfataricus participate in the fundamental pathway of nucleotide catabolism and function to maintain adequate levels of free nitrogenous bases for cellular function. The two highly homologous isozymes display distinct specificities toward nucleoside substrates, and both lack the amino acids employed for activation of the leaving group in the hydrolytic reaction by the NHs characterized thus far. We determined the high-resolution crystal structures of the purine- and pyrimidine-specific NHs from S. solfataricus to reveal that both enzymes belong to NH structural homology group I, despite the different substrate specificities. A Na+ ion is bound at the active site of the pyrimidine-specific NH instead of the prototypical Ca2+, delineating a role of the metals in the catalytic mechanism of NHs in the substrate binding rather than nucleophile activation. A conserved His residue, which regulates product release in other homologous NHs, provides crucial interactions for leaving group activation in the archaeal isozymes. Modeling of the enzyme-substrate interactions suggests that steric exclusion and catalytic selection underlie the orthogonal base specificity of the two isozymes. (Figure Presented).

Original languageEnglish
Pages (from-to)4590-4599
Number of pages10
JournalBiochemistry
Volume51
Issue number22
DOIs
Publication statusPublished - Jun 5 2012

ASJC Scopus subject areas

  • Biochemistry

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