PT  - JOURNAL ARTICLE
AU  - Juliana Roberta Torini
AU  - Larissa Romanello
AU  - Fernanda Aparecida Heleno Batista
AU  - Vitor Hugo Balasco Serrão
AU  - Muhammad Faheem
AU  - Ana Eliza Zeraik
AU  - Louise Bird
AU  - Joanne Nettleship
AU  - Yamini Reddivari
AU  - Ray Owens
AU  - Ricardo DeMarco
AU  - Júlio César Borges
AU  - José Brandão-Neto
AU  - Humberto D’Muniz Pereira
TI  - The molecular structure of <em>Schistosoma mansoni</em> PNP isoform 2 provides insights into the nucleotide selectivity of PNPs
AID  - 10.1101/300533
DP  - 2018 Jan 01
TA  - bioRxiv
PG  - 300533
4099  - http://biorxiv.org/content/early/2018/04/13/300533.short
4100  - http://biorxiv.org/content/early/2018/04/13/300533.full
AB  - Purine nucleoside phosphorylases (PNPs) play an important role in the blood fluke parasite Schistosoma mansoni as a key enzyme of the purine salvage pathway. Here we present the structural and kinetic characterization of a new PNP isoform from S. mansoni, named as SmPNP2. Screening of different ligands using a thermofluorescence approach indicated cytidine and cytosine as potential ligands. The binding of cytosine was confirmed by isothermal titration calorimetry, with a KD of 27 μM, and kinetic parameters for cytidine catalysis were obtained by ITC resulting in a KM of 76.3 μM. SmPNP2 also displays catalytic activity against inosine and adenosine, making it the first described PNP with robust catalytic activity towards both pyrimidines and purines. Crystallographic structures of SmPNP2 with different ligands were obtained and comparison of these structures with the previously described S. mansoni PNP (SmPNP1) provided clues for the unique capability of SmPNP2 to bind pyrimidines. When compared with the structure of SmPNP1, substitutions in the vicinity of SmPNP2 active site alter the architecture of the nucleoside base binding site allowing an alternative binding mode for nucleosides, with a 180° rotation from the canonical binding mode. The remarkable plasticity of this binding site deepens the understanding of the correlation between structure and nucleotide selectivity, offering new ways to analyses PNP activity.Author Summary Schistosoma mansoni is a human parasite dependent on purine salvage for purine bases supply. Purine nucleoside phosphorylase (PNP) is a key enzyme in this pathway. It carries two PNP isoforms, one previously characterized (SmPNP1) and one unknown (SmPNP2). Here we present the crystallographic structure of SmPNP2 and its complex with cytosine, cytidine, ribose-l-phosphate, adenine, hypoxanthine, and tubercidin. Cytidine and cytosine were identified as ligands of SmPNP2 using a thermofluorescence approach. Binding of cytosine was proven by Isothermal Titration Calorimetry (ITC) and cytidine, inosine, and adenosine kinetic parameters were also obtained. Purine bases showed different binding in the active site, rotated 180° from the canonical binding mode. It’s the first report showing a Low Molecular Mass PNP capable of catalyzing both types of nucleotide bases. The SmPNP2 odd behavior sheds a new light on the Schistosoma mansoni’s life cycle metabolic adaptation.