3ODG CRYSTAL STRUCTURE OF XANTHOSINE PHOSPHORYLASE BOUND WITH XANTHINE FROM YERSINIA PSEUDOTUBERCULOSIS TRANSFERASE, STRUCTURAL GENOMICS, PSI-2, PROTEIN STRUCTURE INITIATIVE, NEW YORK SGX RESEARCH CENTER FOR STRUCTURAL GENOMICS, NYSGXRC, PURINE NUCLEOSIDE PHOSPHORYLASE, PURINE NUCLEOSIDE BINDING