engleski

Purine Nucleoside Phosphorylase in a Complex with a Potent Multisubstrate Analogue Inhibitor

Purine nucleoside phosphorylase (PNP, EC 2.4.2.1.) is the key enzyme of the purine salvage pathway. In mammals homotrimeric PNPs catalyse the reversible phosphorolytic cleavage of the glycosidic bond of purine nucelosides and some analogues: purine nucleoside + orthophosphate ↔ base + pentose-1-phosphate. PNP is crucial for the integrity of the immune system and PNP deficiency in humans leads to inhibition of T-cell response. Pharmacologic inhibition of PNP may be useful in the treatment of various autoimmune diseases such as psoriasis, rheumatoid arthritis, multiple sclerosis, other T-cell proliferative disorders and adult T-cell leukemia. Potent membrane-permeable inhibitors of this enzyme are therefore considered as potential immunosuppressive agents.Since the genetic deficiency of PNP has been discovered, great efforts have been made to design inhibitors of PNPs with potential medical applications. The important class of potent ground-state analogue inhibitors of trimeric PNPs is composed of so called multisubstrate analogue inhibitors. These are compounds consisting of three structural parts linked together: purine base, acyclic chain or cyclic moiety and phosphonate or phosphate or other electronegative group. We describe X-ray structure of trimeric calf spleen PNP, highly homologous to the human PNP, with the potent multisubstrate analogue inhibitor 9-(5, 5-difluoro-5 phosphonopentyl)guanine. To investigate inhibitory potential of this compound on human blood T-lymphocytes derived form healthy donor (control) and blood T-lymphocytes derived from subjects affected by psoriasis vulgaris (psoriasis lymphocytes) the MTT-assay was used. Mild or no suppression of control cell growth was observed. In the applied concentration of 10^-7 M to 10^-4 M, the 9-(5, 5-difluoro-5 phosphonopentyl)guanine displayed moderate (20-36% inhibition) to weak (14% inhibition) cytotoxic potency on the psoriasis lymphocytes as compared to control lymphocytes.

purine nucleoside phosphorylase

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