title: Phylogenetic and syntenic data support a single horizontal transference to a Trypanosoma ancestor of a prokaryotic proline racemase implicated in parasite evasion from host defences.
abstract: BACKGROUND
  Proline racemase (PRAC) enzymes of Trypanosoma cruzi (TcPRAC), the agent of Chagas disease, and Trypanosoma vivax (TvPRAC), the agent of livestock trypanosomosis, have been implicated in the B-cells polyclonal activation contributing to immunosuppression and the evasion of host defences. The similarity to prokaryotic PRAC and the absence in Trypanosoma brucei and Trypanosoma congolense have raised many questions about the origin, evolution, and functions of trypanosome PRAC (TryPRAC) enzymes.
  
  
  RESULTS
  We identified TryPRAC homologs as single copy genes per haploid genome in 12 of 15 Trypanosoma species, including T. cruzi and T. cruzi marinkellei, T. dionisii, T. erneyi, T. rangeli, T. conorhini and T. lewisi, all parasites of mammals. Polymorphisms in TcPRAC genes matched T. cruzi genotypes: TcI-TcIV and Tcbat have unique genes, while the hybrids TcV and TcVI contain TcPRACA and TcPRACB from parental TcII and TcIII, respectively. PRAC homologs were identified in trypanosomes from anurans, snakes, crocodiles, lizards, and birds. Most trypanosomes have intact PRAC genes. T. rangeli possesses only pseudogenes, maybe in the process of being lost. T. brucei, T. congolense and their allied species, except the more distantly related T. vivax, have completely lost PRAC genes.
  
  
  CONCLUSIONS
  The genealogy of TryPRAC homologs supports an evolutionary history congruent with the Trypanosoma phylogeny. This finding, together with the synteny of PRAC loci, the relationships with prokaryotic PRAC inferred by taxon-rich phylogenetic analysis, and the absence in trypanosomatids of any other genera or in bodonids or euglenids suggest that a common ancestor of Trypanosoma gained PRAC gene by a single and ancient horizontal gene transfer (HGT) from a Firmicutes bacterium more closely related to Gemella and other species of Bacilli than to Clostridium as previously suggested. Our broad phylogenetic study allowed investigation of TryPRAC evolution over long and short timescales. TryPRAC genes diverged to become species-specific and genotype-specific for T. cruzi and T. rangeli, with resulting genealogies congruent with those obtained using vertically inherited genes. The inventory of TryPRAC genes described here is the first step toward the understanding of the roles of PRAC enzymes in trypanosomes differing in life cycles, virulence, and infection and immune evasion strategies.
authors.affiliation: Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, SP, 05508-900, Brazil. zcaballero1178@yahoo.com.|Instituto de Investigaciones Científicas y Servicios de Alta Tecnología-AIP (INDICASAT-AIP), Ciudad del Saber, Clayon, Panamá. zcaballero1178@yahoo.com.
authors.forename: Zuleima C
authors.initials: ZC
authors.lastname: Caballero
authors.affiliation: Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, SP, 05508-900, Brazil. andreguilherme@usp.br.
authors.forename: Andre G
authors.initials: AG
authors.lastname: Costa-Martins
authors.affiliation: Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, SP, 05508-900, Brazil. mini_exon@hotmail.com.
authors.forename: Robson C
authors.initials: RC
authors.lastname: Ferreira
authors.affiliation: Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, SP, 05508-900, Brazil. alvesjmp@gmail.com.
authors.forename: João M
authors.initials: JM
authors.lastname: P Alves
authors.affiliation: Department of Microbiology and Immunology, Virginia Commonwealth University, Virginia, USA. mgserrano@vcu.edu.
authors.forename: Myrna G
authors.initials: MG
authors.lastname: Serrano
authors.affiliation: Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, SP, 05508-900, Brazil. erney@usp.br.
authors.forename: Erney P
authors.initials: EP
authors.lastname: Camargo
authors.affiliation: Department of Microbiology and Immunology, Virginia Commonwealth University, Virginia, USA. gabuck@vcu.edu.
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Buck
authors.affiliation: Département Infection et Epidemiologie, Institut Pasteur, Laboratoire des Processus Infectieux à Trypanosomatidés, Paris, France. paola.minoprio@pasteur.fr.
authors.forename: Paola
authors.initials: P
authors.lastname: Minoprio
authors.affiliation: Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, SP, 05508-900, Brazil. mmgteix@icb.usp.br.
authors.forename: Marta M
authors.initials: MM
authors.lastname: G Teixeira
mesh_terms: D000591:Amino Acid Isomerases / Q000235:genetics*; D000595:Amino Acid Sequence; D019143:Evolution, Molecular; D000068536:Bacillota / Q000201:enzymology / Q000235:genetics*; D022761:Gene Transfer, Horizontal; D057131:Immune Evasion; D008969:Molecular Sequence Data; D010802:Phylogeny; D015800:Protozoan Proteins / Q000235:genetics*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D026801:Synteny; D014345:Trypanosoma / Q000201:enzymology / Q000235:genetics* / Q000276:immunology
chemical_list: D015800:Protozoan Proteins; D000591:Amino Acid Isomerases; C022451:proline racemase