2isc

<table><tr><td colspan='2'>[[2isc]] is a 6 chain structure with sequence from [https://en.wikipedia.org/wiki/Triva Triva]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=2ISC OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=2ISC FirstGlance]. <br>

</td></tr><tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=223:(3R,4R)-1-[(4-AMINO-5H-PYRROLO[3,2-D]PYRIMIDIN-7-YL)METHYL]-4-(HYDROXYMETHYL)PYRROLIDIN-3-OL'>223</scene>, <scene name='pdbligand=PO4:PHOSPHATE+ION'>PO4</scene></td></tr>

<tr id='activity'><td class="sblockLbl"><b>Activity:</b></td><td class="sblockDat"><span class='plainlinks'>[https://en.wikipedia.org/wiki/Purine-nucleoside_phosphorylase Purine-nucleoside phosphorylase], with EC number [https://www.brenda-enzymes.info/php/result_flat.php4?ecno=2.4.2.1 2.4.2.1] </span></td></tr>

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== Publication Abstract from PubMed ==

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.

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<ref>PMID:17223688</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>

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<div class="pdbe-citations 2isc" style="background-color:#fffaf0;"></div>

== References ==

<references/>

[[Category: Purine-nucleoside phosphorylase]]

[[Category: Triva]]

[[Category: Almo, S C]]

[[Category: Rinaldo-Matthis, A]]

[[Category: Schramm, V L]]

[[Category: Transferase]]