Recent advances in structure and function of cytosolic IMP-GMP specific 5'-nucleotidase II (cN-II).
Cytosolic 5' nucleotidase II (cN-II) catalyses both the hydrolysis of a number of nucleoside monophosphates (e.g., IMP + H₂O--> inosine + Pi), and the phosphate transfer from a nucleoside monophosphate donor to the 5' position of a nucleoside acceptor (e.g., IMP + guanosine --> inosine + GMP). The enzyme protein functions through the formation of a covalent phosphoenzyme intermediate, followed by the phosphate transfer either to water (phosphatase activity) or to a nucleoside (phosphotransferase activity). It has been proposed that cN-II regulates the intracellular concentration of IMP and GMP and the production of uric acid. The enzyme might also have a potential therapeutic importance, since it can phosphorylate some anti-tumoral and antiviral nucleoside analogues that are not substrates of known kinases. In this review we summarise our recent studies on the structure, regulation and function of cN-II. Via a site-directed mutagenesis approach, we have identified the amino acids involved in the catalytic mechanism and proposed a structural model of the active site. A series of in vitro studies suggests that cN-II might contribute to the regulation of 5-phosphoribosyl-1-pyrophosphate (PRPP) level, through the so-called oxypurine cycle, and in the production of intracellular adenosine, formed by ATP degradation.
Ipata
Piero Luigi
PL
Laboratorio di Biochimica, Dipartimento di Biologia, University of Pisa, Via S. Zeno 51, 56100, Pisa, Italy.
Tozzi
Maria Grazia
MG