@ARTICLE{TreeBASE2Ref21819, author = {Felipe Aguilera and Carmel McDougall and Bernard M Degnan}, title = {Origin, evolution and classification of type-3 copper proteins: Lineage-specific gene expansions and losses across the Metazoa}, year = {2013}, keywords = {Type-3 copper proteins, catechol oxidase, tyrosinase, tyrosinase-related protein, hemocyanin, gene expansion, gene loss}, doi = {10.1186/1471-2148-13-96}, url = {http://http://www.biomedcentral.com/1471-2148/13/96/abstract}, pmid = {}, journal = {BMC Evolutionary Biology}, volume = {}, number = {}, pages = {}, abstract = {Background. Tyrosinases, tyrosinase-related proteins, catechol oxidases and hemocyanins comprise the type-3 copper protein family and are involved in a variety of biological processes, including pigment formation, innate immunity and oxygen transport, via the binding of dioxygen. This family is present in the three domains of life, however previous studies have largely focussed on specific metazoan and plant lineages and the origin and early evolution of the family is not well understood. Results. Here, we use genomic, phylogenetic and structural analyses to show that the ancestral type-3 copper protein was secreted (so-called α subclass). The gene encoding this protein underwent two duplication events, the first being prior to the divergence of the unikont eukaryotic lineages and the second being before the diversification of animals. The former duplication gave rise to a cytosolic form (β) and the latter to a membrane-bound form (γ). Structural comparisons reveal that the active site of α and γ forms are covered by aliphatic amino acids, however, the active site of the β form has a highly conserved aromatic residue covering the active site, resulting in differing enzymatic activities between β and α/γ forms. The subsequent evolution of this gene family in modern lineages of multicellular eukaryotes is typified by the loss of one or more of these three subclasses and the lineage-specific expansion of one or both of the remaining subclasses. Conclusions. The diversity of type-3 copper proteins in animals and other eukaryotes is consistent with two ancient gene duplication events leading to α, β and γ subclasses, followed by the differential loss and expansion of one or more of these subclasses in specific kingdoms and phyla, which in turn has led to lineage-specific structural and functional adaptations and constraints. Functionally-classified tyrosinases and hemocyanins are polyphyletic, because the oxygen-carrying hemocyanins in arthropods evolved from a β-subclass tyrosinase while hemocyanins in molluscs and urochordates evolved independently from an α-subclass tyrosinase. The tyrosinases do not form a monophyletic clade. Minor conformational changes at the active site of α, β and γ forms produce type-3 copper proteins with capacities to either carry oxygen (hemocyanins), oxidize diphenols (catechol oxidase) or o-hydroxylate monophenols (tyrosinases). } }

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