Homologia, paralogia e função da DGF-1, uma família gênica específica de Trypanosoma cruzi

• Ano de defesa: 2009
• Autor(a) principal: Kawashita, Silvia Yukie [UNIFESP]
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de São Paulo (UNIFESP)
• Palavras-chave em Português: Entropia de Shannon; Integrinas; Seleção genética; Trypanosoma cruzi
• Link de acesso: http://repositorio.unifesp.br/handle/11600/9695

Surface adhesion proteins are essential for Trypanosoma cruzi invasion of mammalian cells. Here we show that Dispersed Gene Family-1 (DGF-1) members, previously identified as nuclear repeated sequences present in several chromosomes and comprising the third largest T. cruzi-specific gene family, have conserved adhesin motifs including four segments with significant similarity to human beta 7 integrin. Flow cytometry and biotinylation assays with anti-DGF-1 antibodies indicated that, as expected, DGF-1 members are expressed on the trypomastigote surface. The DGF-1 genealogy, inferred using T. cruzi Genome Project data and network phylogeny algorithms, suggests that this gene family is separated in at least three groups with differential distribution of functional domains. To identify which members of this gene family are expressed we used a combined approach of RT-PCR and codon usage profiles, showing that expressed members have a very biased codon usage favoring GC whereas non-expressed members have a homogeneous distribution. Shannon information entropy was used to measure sequence variability and revealed four major high entropy segments in the extracellular domain of DGF-1 overlapping with important putative functional modules of the predicted proteins. Testing for natural selection, however, indicated that these high entropy segments were not under positive selection, which contradicts the notion that positive selection is the cause of high variability in specific domains of a protein relative to other less variable regions in the same molecule. We hypothesize that members of the DGF-1 family are associated with the ability of T. cruzi to bind extracellular matrix proteins, such as fibronectin and laminin, and speculate on mechanisms that would be generating the localized diversity in these molecules in the absence of selection.