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Low exchangeability of selenocysteine, the 21st amino acid, in vertebrate proteins.

ABSTRACT: Selenocysteine (Sec), the 21st amino acid, is incorporated into proteins through the recoding of a termination codon, an inefficient translational process mediated by a complex molecular machinery. Sec is a rare amino acid in extant proteins, chemically similar to cysteine (Cys), found in homologous position to Cys of nonselenoprotein families. Selenoproteins account for the dependence of vertebrates on environmental selenium (Se) and have an important role in several Se-deficiency diseases. Selenoproteins are poorly characterized enzymes and reports on the functional exchangeability of Sec with Cys are limited and controversial. Whether the unique role of Sec in some selenoenzymes illustrates the broader contribution of Se to protein function is unknown (Gromer S, Johansson L, Bauer H, Arscott LD, Rauch S, Ballou DP, Williams CH Jr, Schirmer RH, Arnér ES. 2003. Active sites of thioredoxin reductases: why selenoproteins? Proc Natl Acad Sci USA. 100:12618-12623). Here, we address this question from an evolutionary perspective by the simultaneous identification of the patterns of divergence in almost half a billion years of vertebrate evolution and diversity within the human lineage for the full complement of enzymatic Sec residues in these proteomes. We complete this analysis with data for the homologous Cys residues in the same genomes. Our results indicate concerted purifying selection across Sec and Cys sites in all selenoproteomes, consistent with a unique role of Sec in protein function, low exchangeability, and an unknown degree of functional divergence with Cys homologs. The distinct biochemical properties of Sec, rather than the geographical distribution of Se, global O(2) levels or Sec metabolic cost, appear to play a major role in driving adaptive changes in vertebrate selenoproteomes. A better understanding of the selenoproteomes and neutral evolutionary patterns in other taxa will be necessary to fully assess the generality of this conclusion.

SUBMITTER: Castellano S

PROVIDER: S-EPMC2734155 | biostudies-literature | 2009 Sep

REPOSITORIES: biostudies-literature

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Low exchangeability of selenocysteine, the 21st amino acid, in vertebrate proteins.

Castellano Sergi S Andrés Aida M AM Bosch Elena E Bayes Mònica M Guigó Roderic R Clark Andrew G AG

Molecular biology and evolution 20090601 9

Selenocysteine (Sec), the 21st amino acid, is incorporated into proteins through the recoding of a termination codon, an inefficient translational process mediated by a complex molecular machinery. Sec is a rare amino acid in extant proteins, chemically similar to cysteine (Cys), found in homologous position to Cys of nonselenoprotein families. Selenoproteins account for the dependence of vertebrates on environmental selenium (Se) and have an important role in several Se-deficiency diseases. Sel ...[more]

PMID: 19487332

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Project description:Adequate modeling of mitochondrial sequence evolution is an essential component of mitochondrial phylogenomics (comparative mitogenomics). There is wide recognition within the field that lineage-specific aspects of mitochondrial evolution should be accommodated through lineage-specific amino-acid exchangeability matrices (e.g., mtMam for mammalian data). However, such a matrix must be applied to all sites and this implies that all sites are subject to the same, or largely similar, evolutionary constraints. This assumption is unjustified. Indeed, substantial differences are expected to arise from three-dimensional structures that impose different physiochemical environments on individual amino acid residues. The objectives of this paper are (1) to investigate the extent to which amino acid evolution varies among sites of mitochondrial proteins, and (2) to assess the potential benefits of explicitly modeling such variability. To achieve this, we developed a novel method for partitioning sites based on amino acid physiochemical properties. We apply this method to two datasets derived from complete mitochondrial genomes of mammals and fish, and use maximum likelihood to estimate amino acid exchangeabilities for the different groups of sites. Using this approach we identified large groups of sites evolving under unique physiochemical constraints. Estimates of amino acid exchangeabilities differed significantly among such groups. Moreover, we found that joint estimates of amino acid exchangeabilities do not adequately represent the natural variability in evolutionary processes among sites of mitochondrial proteins. Significant improvements in likelihood are obtained when the new matrices are employed. We also find that maximum likelihood estimates of branch lengths can be strongly impacted. We provide sets of matrices suitable for groups of sites subject to similar physiochemical constraints, and discuss how they might be used to analyze real data. We also discuss how the general approach might be employed to improve a variety of mitogenomic-based research activities.

Dataset Information

Low exchangeability of selenocysteine, the 21st amino acid, in vertebrate proteins.

Publications

Low exchangeability of selenocysteine, the 21st amino acid, in vertebrate proteins.

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