2isc
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(New page: 200px<br /><applet load="2isc" size="350" color="white" frame="true" align="right" spinBox="true" caption="2isc, resolution 2.700Å" /> '''Crystal stucture of...)
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Revision as of 13:00, 23 January 2008
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Crystal stucture of Purine Nucleoside Phosphorylase from Trichomonas vaginalis with DADMe-Imm-A
Overview
Trichomonas vaginalis is a parasitic protozoan purine auxotroph possessing, a unique purine salvage pathway consisting of a bacterial type purine, nucleoside phosphorylase (PNP) and a purine nucleoside kinase. Thus, T., vaginalis PNP (TvPNP) functions in the reverse direction relative to the, PNPs in other organisms. Immucillin-A (ImmA) and DADMe-Immucillin-A, (DADMe-ImmA) are transition state mimics of adenosine with geometric and, electrostatic features that resemble early and late transition states of, adenosine at the transition state stabilized by TvPNP. ImmA demonstrates, slow-onset tight-binding inhibition with TvPNP, to give an equilibrium, dissociation constant of 87 pM, an inhibitor release half-time of 17.2, min, and a Km/Kd ratio of 70,100. DADMe-ImmA resembles a late, ribooxacarbenium ion transition state for TvPNP to give a dissociation, constant of 30 pM, an inhibitor release half-time of 64 min, and a Km/Kd, ratio of 203,300. The tight binding of DADMe-ImmA supports a late SN1, transition state. Despite their tight binding to TvPNP, ImmA and, DADMe-ImmA are weak inhibitors of human and P. falciparum PNPs. The, crystal structures of the TvPNP x ImmA x PO4 and TvPNP x DADMe-ImmA x PO4, ternary complexes differ from previous structures with substrate, analogues. The tight binding with DADMe-ImmA is in part due to a 2.7 A, ionic interaction between a PO4 oxygen and the N1' cation of the, hydroxypyrrolidine and is weaker in the TvPNP x ImmA x PO4 structure at, 3.5 A. However, the TvPNP x ImmA x PO4 structure includes hydrogen bonds, between the 2'-hydroxyl and the protein that are not present in TvPNP x, DADMe-ImmA x PO4. These structures explain why DADMe-ImmA binds tighter, than ImmA. Immucillin-H is a 12 nM inhibitor of TvPNP but a 56 pM, inhibitor of human PNP. And this difference is explained by isotope-edited, difference infrared spectroscopy with [6-18O]ImmH to establish that O6 is, the keto tautomer in TvPNP x ImmH x PO4, causing an unfavorable, leaving-group interaction.
About this Structure
2ISC is a Protein complex structure of sequences from Trichomonas vaginalis with and as ligands. Active as Purine-nucleoside phosphorylase, with EC number 2.4.2.1 Full crystallographic information is available from OCA.
Reference
Inhibition and structure of Trichomonas vaginalis purine nucleoside phosphorylase with picomolar transition state analogues., Rinaldo-Matthis A, Wing C, Ghanem M, Deng H, Wu P, Gupta A, Tyler PC, Evans GB, Furneaux RH, Almo SC, Wang CC, Schramm VL, Biochemistry. 2007 Jan 23;46(3):659-68. PMID:17223688
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