title: Analysis of two Schistosoma mansoni uridine phosphorylases isoforms suggests the emergence of a protein with a non-canonical function.
abstract: Reports of Schistosoma mansoni strains resistant to praziquantel, the only therapeutic strategy available for the treatment of schistosomiasis, have motivated the scientific community towards the search for new possible therapies. Biochemical characterization of the parasite's metabolism is an essential component for the rational development of new therapeutic alternatives. One of the so far uncharacterized enzymes is uridine phosphorylase (UP) (EC 2.4.2.3), for which the parasite genome presents two isoforms (SmUPa and SmUPb) that share 92% sequence identity. In this paper, we present crystal structures for SmUPa and SmUPb in their free states as well as bound to different ligands. This we have complemented by enzyme kinetic characterization and phylogenetic analyses. Both enzymes present an overall fold and active site structure similar to other known UPs. The kinetic analyses showed conclusively that SmUPa is a regular uridine phosphorylase but by contrast SmUPb presented no detectable activity. This is particularly noteworthy given the high level of sequence identity between the two isoforms and is probably the result of the significant differences observed for SmUPb in the vicinity of the active site itself, suggesting that it is not a UP at all. On the other hand, it was not possible to identify an alternative function for SmUPb, although our phylogenetic analyses and expression data suggest that SmUPb is still functional and plays a role in parasite metabolism. The unusual UPb isoform may open up new opportunities for understanding unique features of S. mansoni metabolism.
authors.affiliation: São Carlos Institute of Physics, São Paulo University, São Carlos, São Paulo, Brazil.
authors.forename: Antônio Marinho
authors.initials: AM
authors.lastname: da Silva Neto
authors.affiliation: São Carlos Institute of Physics, São Paulo University, São Carlos, São Paulo, Brazil.
authors.forename: Juliana Roberta
authors.initials: JR
authors.lastname: Torini de Souza
authors.affiliation: São Carlos Institute of Physics, São Paulo University, São Carlos, São Paulo, Brazil.
authors.forename: Larissa
authors.initials: L
authors.lastname: Romanello
authors.affiliation: Brazilian Nanotechnology National Laboratory, CNPEN, Campinas, São Paulo, Brazil.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Cassago
authors.affiliation: São Carlos Institute of Physics, São Paulo University, São Carlos, São Paulo, Brazil.
authors.forename: Vitor Hugo Balasco
authors.initials: VH
authors.lastname: Serrão
authors.affiliation: São Carlos Institute of Physics, São Paulo University, São Carlos, São Paulo, Brazil.
authors.forename: Ricardo
authors.initials: R
authors.lastname: DeMarco
authors.affiliation: Diamond Light Source, Harwell Science and Inovation Campus, Didcot, UK.
authors.forename: José
authors.initials: J
authors.lastname: Brandão-Neto
authors.affiliation: São Carlos Institute of Physics, São Paulo University, São Carlos, São Paulo, Brazil.
authors.forename: Richard Charles
authors.initials: RC
authors.lastname: Garratt
authors.affiliation: São Carlos Institute of Physics, São Paulo University, São Carlos, São Paulo, Brazil. Electronic address: hmuniz@ifsc.usp.br.
authors.forename: Humberto D'Muniz
authors.initials: HD
authors.lastname: Pereira
mesh_terms: D000818:Animals; D018360:Crystallography, X-Ray; D015801:Helminth Proteins / Q000737:chemistry*; D007527:Isoenzymes; D000072417:Protein Domains; D012550:Schistosoma mansoni / Q000201:enzymology*; D014543:Uridine Phosphorylase / Q000737:chemistry*
chemical_list: D015801:Helminth Proteins; D007527:Isoenzymes; D014543:Uridine Phosphorylase
keywords: Isoforms; Pyrimidine metabolism; Schistosoma mansoni; Uridine phosphorylase; X-ray crystallography