| 其他摘要 | Lipocalins are widespread and diverse proteins which bind and transport small hydrophobic molecules. In SCOP, the superfamily consists of 8 different families, which are RBP(Retinol binding protein-like), FABP(Fatty acid binding protein-like), Triabin(Thrombin inhibitor), Hypothetical protein YodA, Hypothetical protein YwiB, PAD(Phenolic acid decarboxylase) , Dinoflagellate luciferase repeat and Rv2717c-like. It is considerable difficulty to produce a phylogeny of all strongly divergent lipocalin protein sequences. In this study, we analyzed the structural and functional evolution between and among every family, and discussed the possible evolution history of this superfamily. The un-rooted NJ-tree of PAD family showed that different PAD in different species assigned to each branch, which suggested that all PAD proteins evolved from a single common bacteria ancestor, then they divergent in different species. Besides, in the tree only 2 PAD proteins (ferulate decarboxylase, FDC) in Trichomonas, they may be the products of gene horizontal transfer. LCF family proteins evolutionary analysis show that LCFs are highly conservered and share a common ancestor. The tree split into two branches obviously, which suggest LCFs experience a great divergent at one point, possibly after Lp and Pr diverged.Taken together,Our results suggested that these structural resemblance superfamily proteins might reflect a process of evolutionary convergence to optimize a similar lingand bingding function; in which, only Triabin and RBP family were divergent from a common lipocalin ancestor. The retinoids are a class of chemical compounds that are related chemically to vitamin A, which is an essential nutrient that plays a key role in vision, cell growth and differentiation. In vivo, retinoid needs to bind with specific proteins to perform functions. Plasma retinol-binding protein (RBP), epididymal retinoic acid binding protein (ERABP), cellular retinol-binding proteins (CRBPs) and cellular retinoic acid binding proteins(CRABPs) are specific carriers of the retinoids in body fluids and within the cell, respectively. As lipocalins superfamily protein, all these proteins possess similarly structures, which consist of a β-strand barrel and could bind similar retinoids ligand. But the binding orientation and mechanism is different. In this paper we analysis this phenomena and advance a transport model of retinoids. Our results show that retinoids transport proteins bind identical ligands in totally different ways. Except the different binding position, none of the ligand-binding amino acids is conserved between those transport proteins. But in every specific binding protein, the amino acid involving with ligand binding is conserved. |
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