2i4t: Difference between revisions

|PDB= 2i4t |SIZE=350|CAPTION= <scene name='initialview01'>2i4t</scene>, resolution 2.74&Aring;

|SITE=  

|LIGAND= <scene name='pdbligand=PO4:PHOSPHATE+ION'>PO4</scene> and <scene name='pdbligand=UA2:3,4-PYRROLIDINEDIOL,2-(4-AMINO-5H-PYRROLO[3,2-D]PYRIMIDIN-7-YL)-5-(HYDROXYMETHYL)-2S,3S,4R,5R'>UA2</scene>

|ACTIVITY= [http://en.wikipedia.org/wiki/Purine-nucleoside_phosphorylase Purine-nucleoside phosphorylase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=2.4.2.1 2.4.2.1]  

|GENE=  

 

 

==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.

 

2I4T is a [[Protein complex]] structure of sequences from [http://en.wikipedia.org/wiki/Trichomonas_vaginalis Trichomonas vaginalis]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=2I4T OCA].

 

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:[http://www.ncbi.nlm.nih.gov/pubmed/17223688 17223688]

[[Category: Purine-nucleoside phosphorylase]]

[[Category: Almo, S C.]]

[[Category: Rinaldo-Matthis, A.]]

[[Category: Schramm, V L.]]