Plasmodium falciparum purine nucleoside phosphorylase: crystal structures, immucillin inhibitors, and dual catalytic function.
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.
Shi
Wuxian
W
Department of Biochemistry, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York 10461, USA.
Ting
Li-Min
LM
Kicska
Gregory A
GA
Lewandowicz
Andrzej
A
Tyler
Peter C
PC
Evans
Gary B
GB
Furneaux
Richard H
RH
Kim
Kami
K
Almo
Steve C
SC
Schramm
Vern L
VL
D000818:Animals; D002384:Catalysis; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000737:chemistry; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008778:Methylthioinosine / Q000031:analogs & derivatives* / Q000378:metabolism; D015394:Molecular Structure; D010963:Plasmodium falciparum / Q000201:enzymology*; D011684:Purine Nucleosides; D011683:Purine-Nucleoside Phosphorylase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D011744:Pyrimidinones / Q000737:chemistry; D011758:Pyrroles / Q000737:chemistry
D004791:Enzyme Inhibitors; D011684:Purine Nucleosides; D011744:Pyrimidinones; D011758:Pyrroles; C038025:5'-methylthioinosine; D008778:Methylthioinosine; C113101:forodesine; D011683:Purine-Nucleoside Phosphorylase