RESUMO
Cysteine (Cys) is regarded as the most conservative amino acid in nature, something that does not occur in the tunicate Oikopleura dioica, where this amino acid is one of the fastest evolving. In this work we analyze some of the causes of this intriguing absence of conservation. Considering the well-known stabilizing role of Cys, it was first investigated whether the lack of conservation was accompanied by an increase in intrinsic protein disorder. In contrast to expectations, it was found that O. dioica is the chordate that has the lowest levels of intrinsic disorder, while vertebrates (represented by Bos taurus) contain the most disordered proteins. Oikopleura proteins are shorter than their homologs in other Chordates (Ciona and B. taurus proteins are respectively 11% and 18% longer). This process of protein shortening was more intense in intrinsic disordered regions. As a result proteins became not only shorter but also more compact. It is also reported here that the conservation/divergence behavior of Cys depends on whether they are located in ordered or disordered regions. In the four species analyzed, disordered Cys are majorly (> 75%) not conserved at all. Ordered Cys instead, are much more free to diverge in Oikopleura than in the other chordates. We hypothesize that the preferential deletion of disordered regions resulted in a decreased protein disorder and a direct elimination (by deletion) of many ancestral Cys. Besides, the alterations (shortening or complete elimination) of some disordered regions (loops/random coils) probably promoted further Cys evolutionary volatility, because some ancestral Cys (and other amino acids which play a role in stability like Trp) located outside deleted regions became redundant due to the loss of their stabilizing partners.
Assuntos
Evolução Biológica , Cisteína/análogos & derivados , Regulação da Expressão Gênica/fisiologia , Proteínas/metabolismo , Urocordados/genética , Urocordados/metabolismo , Animais , Cisteína/metabolismo , Proteínas/genéticaRESUMO
The mitochondrion role changes during the digenetic life cycle of African trypanosomes. Owing to the low abundance of glucose in the insect vector (tsetse flies) the parasites are dependent upon a fully functional mitochondrion, capable of performing oxidative phosphorylation. Nevertheless, inside the mammalian host (bloodstream forms), which is rich in nutrients, parasite proliferation relies on glycolysis, and the mitochondrion is partially redundant. In this work we perform a comparative study of the mitochondrial genome (kinetoplast) in different strains of Trypanosoma vivax. The comparison was conducted between a West African strain that goes through a complete life cycle and two American strains that are mechanically transmitted (by different vectors) and remain as bloodstream forms only. It was found that while the African strain has a complete and apparently fully functional kinetoplast, the American T. vivax strains have undergone a drastic process of mitochondrial genome degradation, in spite of the recent introduction of these parasites in America. Many of their genes exhibit different types of mutations that are disruptive of function such as major deletions, frameshift causing indels and missense mutations. Moreover, all but three genes (A6-ATPase, RPS12 and MURF2) are not edited in the American strains, whereas editing takes place normally in all (editable) genes from the African strain. Two of these genes, A6-ATPase and RPS12, are known to play an essential function during bloodstream stage. Analysis of the minicircle population shows that its diversity has been greatly reduced, remaining mostly those minicircles that carry guide RNAs necessary for the editing of A6-ATPase and RPS12. The fact that these two genes remain functioning normally, as opposed to that reported in Trypanosoma brucei-like trypanosomes that restrict their life cycle to the bloodstream forms, along with other differences, is indicative that the American T. vivax strains are following a novel evolutionary pathway.