Purine nucleoside phosphorylase (PNP) from
Escherichia coli is a homohexamer that catalyses the phosphorolytic cleavage of the glycosidic bond of purine nucleosides. The first crystal structure of the ternary complex of this enzyme (with a phosphate ion and formycin A), which is biased by neither the presence of an inhibitor nor sulfate as a precipitant, is presented. The structure reveals, in some active
sites, an unexpected and never before observed
binding site for phosphate and exhibits a stoichiometry of two phosphate molecules per enzyme subunit. Moreover, in these active
sites, the phosphate and nucleoside molecules are found not to be in direct contact. Rather, they are bridged by three water molecules that occupy the 鈥渟tandard鈥?phosphate
binding site.
Structured summary of protein interactions
and by ()