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CRYSTAL STRUCTURE OF M. TUBERCULOSIS PNP IN COMPLEX WITH IMINORIBITOL, 9-DEAZAHYPOXANTHINE AND PHOSPHATE ION
Structural highlights
FunctionPUNA_MYCTU 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. Cleaves guanosine and inosine (By similarity). Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedA structural genomics comparison of purine nucleoside phosphorylases (PNPs) indicated that the enzyme encoded by Mycobacterium tuberculosis (TB-PNP) resembles the mammalian trimeric structure rather than the bacterial hexameric PNPs. The crystal structure of M. tuberculosis PNP in complex with the transition-state analogue immucillin-H (ImmH) and inorganic phosphate was solved at 1.75 A resolution and confirms the trimeric structure. Binding of the inhibitor occurs independently at the three catalytic sites, unlike mammalian PNPs which demonstrate negative cooperativity in ImmH binding. Reduced subunit interface contacts for TB-PNP, compared to the mammalian enzymes, correlate with the loss of the cooperative inhibitor binding. Mammalian and TB-PNPs both exhibit slow-onset inhibition and picomolar dissociation constants for ImmH. The structure supports a catalytic mechanism of reactant destabilization by neighboring group electrostatic interactions, transition-state stabilization, and leaving group activation. Despite an overall amino acid sequence identity of 33% between bovine and TB-PNPs and almost complete conservation in active site residues, one catalytic site difference suggests a strategy for the design of transition-state analogues with specificity for TB-PNP. The structure of TB-PNP was also solved to 2.0 A with 9-deazahypoxanthine (9dHX), iminoribitol (IR), and PO(4) to reconstruct the ImmH complex with its separate components. One subunit of the trimer has 9dHX, IR, and PO(4) bound, while the remaining two subunits contain only 9dHX. In the filled subunit, 9dHX retains the contacts found in the ImmH complex. However, the region of IR that corresponds to the oxocarbenium ion is translocated in the direction of the reaction coordinate, and the nucleophilic phosphate rotates away from the IR group. Loose packing of the pieces of ImmH in the catalytic site establishes that covalent connectivity in ImmH is required to achieve the tightly bound complex. Structures of purine nucleoside phosphorylase from Mycobacterium tuberculosis in complexes with immucillin-H and its pieces.,Shi W, Basso LA, Santos DS, Tyler PC, Furneaux RH, Blanchard JS, Almo SC, Schramm VL Biochemistry. 2001 Jul 27;40(28):8204-15. PMID:11444966[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences | ||||||||||||||||||||
