title: Basal Gnathostomes provide unique insights into the evolution of vitamin B12 binders.
abstract: The uptake and transport of vitamin B12 (cobalamin; Cbl) in mammals involves a refined system with three evolutionarily related transporters: transcobalamin 1 (Tcn1), transcobalamin 2 (Tcn2), and the gastric intrinsic factor (Gif). Teleosts have a single documented binder with intermediate features to the human counterparts. Consequently, it has been proposed that the expansion of Cbl binders occurred after the separation of Actinopterygians. Here, we demonstrate that the diversification of this gene family took place earlier in gnathostome ancestry. Our data indicates the presence of single copy orthologs of the Sarcopterygii/Tetrapoda duplicates Tcn1 and Gif, and Tcn2, in Chondrichthyes. In addition, a highly divergent Cbl binder was found in the Elasmobranchii. We unveil a complex scenario forged by genome, tandem duplications and lineage-specific gene loss. Our findings suggest that from an ancestral transporter, exhibiting large spectrum and high affinity binding, highly specific Cbl transporters emerged through gene duplication and mutations at the binding pocket.
authors.affiliation: CIIMAR-Interdisciplinary Centre of Marine and Environmental Research, CIMAR Associate Laboratory, UPorto-University of Porto, Portugal ICBAS-Institute of Biomedical Sciences Abel Salazar, UPorto-University of Porto, Portugal.
authors.forename: Mónica
authors.initials: M
authors.lastname: Lopes-Marques
authors.affiliation: CIIMAR-Interdisciplinary Centre of Marine and Environmental Research, CIMAR Associate Laboratory, UPorto-University of Porto, Portugal.
authors.forename: Raquel
authors.initials: R
authors.lastname: Ruivo
authors.affiliation: CIIMAR-Interdisciplinary Centre of Marine and Environmental Research, CIMAR Associate Laboratory, UPorto-University of Porto, Portugal.
authors.forename: Inês
authors.initials: I
authors.lastname: Delgado
authors.affiliation: CIIMAR-Interdisciplinary Centre of Marine and Environmental Research, CIMAR Associate Laboratory, UPorto-University of Porto, Portugal Department of Biology, Wilfred Laurier University-Waterloo, Ontario, Canada.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Wilson
authors.affiliation: Woods Hole Oceanographic Institution, Woods Hole, Massachusetts.
authors.forename: Neelakanteswar
authors.initials: N
authors.lastname: Aluru
authors.affiliation: CIIMAR-Interdisciplinary Centre of Marine and Environmental Research, CIMAR Associate Laboratory, UPorto-University of Porto, Portugal Department of Biology, Faculty of Sciences, UPorto-University of Porto, Portugal filipe.castro@ciimar.up.pt.
authors.forename: L Filipe C
authors.initials: LF
authors.lastname: Castro
mesh_terms: D000818:Animals; D019143:Evolution, Molecular; D005399:Fishes / Q000235:genetics*; D006801:Humans; D016013:Likelihood Functions; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D026801:Synteny / Q000235:genetics; D014155:Transcobalamins / Q000235:genetics*
chemical_list: D014155:Transcobalamins
keywords: cobalamin transport; genome duplications; gnathostomes