1RR6: Structure Of Human Purine Nucleoside Phosphorylase In Complex With Immucillin-H And Phosphate

Purine nucleoside phosphorylase from Plasmodium falciparum (PfPNP) is an anti-malarial target based on the activity of Immucillins. The crystal structure of PfPNP.Immucillin-H (ImmH).SO(4) reveals a homohexamer with ImmH and SO(4) bound at each catalytic site. A solvent-filled cavity close to the 5'-hydroxyl group of ImmH suggested that PfPNP can accept additional functional groups at the 5'-carbon. Assays established 5'-methylthioinosine (MTI) as a substrate for PfPNP. MTI is not found in human metabolism. These properties of PfPNP suggest unusual purine pathways in P. falciparum and provide structural and mechanistic foundations for the design of malaria-specific transition state analogue inhibitors. 5'-Methylthio-Immucillin-H (MT-ImmH) was designed to resemble the transition state of PfPNP and binds to PfPNP and human-PNP with K(d) values of 2.7 and 303 nm, respectively, to give a discrimination factor of 112. MT-ImmH is the first inhibitor that favors PfPNP inhibition. The structure of PfPNP.MT-ImmH.SO(4) shows that the hydrophobic methylthio group inserts into a hydrophobic region adjacent to the more hydrophilic 5'-hydroxyl binding site of ImmH. The catalytic features of PfPNP indicate a dual cellular function in purine salvage and polyamine metabolism. Combined metabolic functions in a single enzyme strengthen the rationale for targeting PfPNP in anti-malarial action.
PDB ID: 1RR6Download
MMDB ID: 31752
PDB Deposition Date: 2003/12/8
Updated in MMDB: 2007/10
Experimental Method:
x-ray diffraction
Resolution: 2.5  Å
Source Organism:
Similar Structures:
Biological Unit for 1RR6: trimeric; determined by author and by software (PISA,PQS)
Molecular Components in 1RR6
Label Count Molecule
Proteins (3 molecules)
Purine Nucleoside Phosphorylase(Gene symbol: PNP)
Molecule annotation
Chemicals (12 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB