Characterization of selenium containing proteins in the coral Acropora millepora

Zou, Huibin (2011) Characterization of selenium containing proteins in the coral Acropora millepora. PhD thesis, James Cook University.

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Selenium (Se) and Se-containing proteins are believed to be involved in many physiological processes. Recent studies have revealed complex repertoires of Se containing proteins in mammals, of which some (known as selenoproteins) contain selenocysteine (Sec; encoded by in-frame UGA codons) and others in which the selenium is bound (selenium binding proteins; SeBPs) without selenoproteins. There have been few studies to date on the selenium protein complements of non-Bilateria animals, and many of the non-Bilateria selenoprotein genes in the public sequence databases are mis-annotated. The main objective of the work described in this thesis was to describe the selenoprotein and selenium-binding protein repertoire of the coral Acropora millepora, a representative non-Bilateria animal and to investigate aspects of the expression of some of the corresponding genes. These studies should not only provide evolutionary insights into selenium biology, but also be relevant to the physiology of coral stress.

To achieve these goals, phylogenetic tools were used to survey the repertoires of selenium-containing proteins in A. millepora and other model organisms, qPCR and immunohistochemistry employed to follow changes in the expression of genes encoding non-enzymatic selenium containing proteins under experimental manipulation, bioinformatics tools used to model the structure of proteins of interest, and chemical tools employed to analyze the Se binding ability of recombinant selenium binding protein towards the inorganic Se in vitro.

The evolutionary studies summarized in Chapter 2 show that in the known invertebrates which have been studied their selenium components, the coral A. millepora has the most complex selenium repertoire (21 Sec-containing selenoproteins and 2 selenium binding proteins); other cnidarians also contain complex selenium repertoires. These results suggest that most of the known selenium components seen in bilaterian animals predate the bilaterian-cnidarian split. In Chapter 3 we report that the expression of several non-enzymatic selenium containing proteins in the coral A. millepora is highly up-regulated by oxidants, suggesting physiology roles for these selenium components in redox regulation.

Studies in Chapter 4 and 5 focused on the A. millepora 56 kDa SeBPs (amSeBPs). Sequence analysis and structure modeling revealed that the conserved cysteine residues that are characteristic of these proteins, together with nearby motifs, cluster at the centre of the monomer protein models. The amSeBPs were ubiquitously expressed and markedly up-regulated at the planula and presettlement stages. Immunolocalisation experiments imply that the amSeBPs are enriched in adult A. millepora gastrodermal tissue that is adjacent to Symbiodinium. The in vitro selenite/amSeBP binding assays showed that the binding of inorganic selenium by amSeBP is dependent on the redox state. These studies imply that the positions of the redox sensitive cysteine residues and nearby motifs are critical for amSeBP function; these constraints presumably underlie the high level of sequence conservation of the 56 kDa SeBP sequences among animals, plants and even microorganisms.

In summary, these results imply important roles for the selenium containing proteins that are abundant in A. millepora. Although some of these proteins have been systematically characterized and implicated in redox metabolism, the mechanistic details remain unclear. To date, functional studies have focused mainly on mammalian Se proteins. Functional analyses in non-Bilateria animals could shed some light on the significance of Se-proteins and selenium biology more broadly.

Item ID: 29162
Item Type: Thesis (PhD)
Keywords: selenium; selenoprotein genes; redox metabolism; Acropora millepora; non-Bilateria animals; selenium containing proteins
Date Deposited: 05 Sep 2013 21:39
FoR Codes: 06 BIOLOGICAL SCIENCES > 0601 Biochemistry and Cell Biology > 060102 Bioinformatics @ 50%
06 BIOLOGICAL SCIENCES > 0601 Biochemistry and Cell Biology > 060199 Biochemistry and Cell Biology not elsewhere classified @ 50%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 100%
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