Structural highlights
Disease
PNPH_HUMAN Defects in PNP are the cause of purine nucleoside phosphorylase deficiency (PNPD) [MIM:613179. It leads to a severe T-cell immunodeficiency with neurologic disorder in children.[1] [2] [3]
Function
PNPH_HUMAN The purine nucleoside phosphorylases catalyze the phosphorolytic breakdown of the N-glycosidic bond in the beta-(deoxy)ribonucleoside molecules, with the formation of the corresponding free purine bases and pentose-1-phosphate.[4]
Publication Abstract from PubMed
Heavy-enzyme isotope effects (15N-, 13C-, and 2H-labeled protein) explore mass-dependent vibrational modes linked to catalysis. Transition path-sampling (TPS) calculations have predicted femtosecond dynamic coupling at the catalytic site of human purine nucleoside phosphorylase (PNP). Coupling is observed in heavy PNPs, where slowed barrier crossing caused a normal heavy-enzyme isotope effect (kchemlight/kchemheavy > 1.0). We used TPS to design mutant F159Y PNP, predicted to improve barrier crossing for heavy F159Y PNP, an attempt to generate a rare inverse heavy-enzyme isotope effect (kchemlight/kchemheavy < 1.0). Steady-state kinetic comparison of light and heavy native PNPs to light and heavy F159Y PNPs revealed similar kinetic properties. Pre-steady-state chemistry was slowed 32-fold in F159Y PNP. Pre-steady-state chemistry compared heavy and light native and F159Y PNPs and found a normal heavy-enzyme isotope effect of 1.31 for native PNP and an inverse effect of 0.75 for F159Y PNP. Increased isotopic mass in F159Y PNP causes more efficient transition state formation. Independent validation of the inverse isotope effect for heavy F159Y PNP came from commitment to catalysis experiments. Most heavy enzymes demonstrate normal heavy-enzyme isotope effects, and F159Y PNP is a rare example of an inverse effect. Crystal structures and TPS dynamics of native and F159Y PNPs explore the catalytic-site geometry associated with these catalytic changes. Experimental validation of TPS predictions for barrier crossing establishes the connection of rapid protein dynamics and vibrational coupling to enzymatic transition state passage.
Catalytic-site design for inverse heavy-enzyme isotope effects in human purine nucleoside phosphorylase.,Harijan RK, Zoi I, Antoniou D, Schwartz SD, Schramm VL Proc Natl Acad Sci U S A. 2017 Jun 20;114(25):6456-6461. doi:, 10.1073/pnas.1704786114. Epub 2017 Jun 5. PMID:28584087[5]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
See Also
References
- ↑ Williams SR, Gekeler V, McIvor RS, Martin DW Jr. A human purine nucleoside phosphorylase deficiency caused by a single base change. J Biol Chem. 1987 Feb 15;262(5):2332-8. PMID:3029074
- ↑ Aust MR, Andrews LG, Barrett MJ, Norby-Slycord CJ, Markert ML. Molecular analysis of mutations in a patient with purine nucleoside phosphorylase deficiency. Am J Hum Genet. 1992 Oct;51(4):763-72. PMID:1384322
- ↑ Pannicke U, Tuchschmid P, Friedrich W, Bartram CR, Schwarz K. Two novel missense and frameshift mutations in exons 5 and 6 of the purine nucleoside phosphorylase (PNP) gene in a severe combined immunodeficiency (SCID) patient. Hum Genet. 1996 Dec;98(6):706-9. PMID:8931706
- ↑ Ealick SE, Rule SA, Carter DC, Greenhough TJ, Babu YS, Cook WJ, Habash J, Helliwell JR, Stoeckler JD, Parks RE Jr, et al.. Three-dimensional structure of human erythrocytic purine nucleoside phosphorylase at 3.2 A resolution. J Biol Chem. 1990 Jan 25;265(3):1812-20. PMID:2104852
- ↑ Harijan RK, Zoi I, Antoniou D, Schwartz SD, Schramm VL. Catalytic-site design for inverse heavy-enzyme isotope effects in human purine nucleoside phosphorylase. Proc Natl Acad Sci U S A. 2017 Jun 20;114(25):6456-6461. doi:, 10.1073/pnas.1704786114. Epub 2017 Jun 5. PMID:28584087 doi:http://dx.doi.org/10.1073/pnas.1704786114
