title: A single rainbow trout cobalamin-binding protein stands in for three human binders.
abstract: Cobalamin uptake and transport in mammals are mediated by three cobalamin-binding proteins: haptocorrin, intrinsic factor, and transcobalamin. The nature of cobalamin-binding proteins in lower vertebrates remains to be elucidated. The aim of this study was to characterize the cobalamin-binding proteins of the rainbow trout (Oncorhynchus mykiss) and to compare their properties with those of the three human cobalamin-binding proteins. High cobalamin-binding capacity was found in trout stomach (210 pmol/g), roe (400 pmol/g), roe fluid (390 nmol/liter), and plasma (2500 nmol/liter). In all cases, it appeared to be the same protein based on analysis of partial sequences and immunological responses. The trout cobalamin-binding protein was purified from roe fluid, sequenced, and further characterized. Like haptocorrin, the trout cobalamin-binding protein was stable at low pH and had a high binding affinity for the cobalamin analog cobinamide. Like haptocorrin and transcobalamin, the trout cobalamin-binding protein was present in plasma and recognized ligands with altered nucleotide moiety. Like intrinsic factors, the trout cobalamin-binding protein was present in the stomach and resisted degradation by trypsin and chymotrypsin. It also resembled intrinsic factor in the composition of conserved residues in the primary cobalamin-binding site in the C terminus. The trout cobalamin-binding protein was glycosylated and displayed spectral properties comparable with those of haptocorrin and intrinsic factor. In conclusion, only one soluble cobalamin-binding protein was identified in the rainbow trout, a protein that structurally behaves like an intermediate between the three human cobalamin-binding proteins.
authors.affiliation: Department of Clinical Biochemistry, Aarhus University Hospital, 8000 Aarhus, Denmark. evagreibe@gmail.com
authors.forename: Eva
authors.initials: E
authors.lastname: Greibe
authors.forename: Sergey
authors.initials: S
authors.lastname: Fedosov
authors.forename: Boe S
authors.initials: BS
authors.lastname: Sorensen
authors.forename: Peter
authors.initials: P
authors.lastname: Højrup
authors.forename: Steen S
authors.initials: SS
authors.lastname: Poulsen
authors.forename: Ebba
authors.initials: E
authors.lastname: Nexo
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003208:Concanavalin A / Q000737:chemistry; D005786:Gene Expression Regulation; D006031:Glycosylation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007437:Intrinsic Factor / Q000737:chemistry; D023421:Models, Animal; D008969:Molecular Sequence Data; D017686:Oncorhynchus mykiss; D010802:Phylogeny; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D014155:Transcobalamins / Q000737:chemistry / Q000378:metabolism*; D014803:Vitamin B Complex / Q000737:chemistry
chemical_list: D014155:Transcobalamins; D003208:Concanavalin A; D014803:Vitamin B Complex; D007437:Intrinsic Factor