title: Early chordate origin of the vertebrate integrin αI domains.
abstract: Half of the 18 human integrins α subunits have an inserted αI domain yet none have been observed in species that have diverged prior to the appearance of the urochordates (ascidians). The urochordate integrin αI domains are not human orthologues but paralogues, but orthologues of human αI domains extend throughout later-diverging vertebrates and are observed in the bony fish with duplicate isoforms. Here, we report evidence for orthologues of human integrins with αI domains in the agnathostomes (jawless vertebrates) and later diverging species. Sequence comparisons, phylogenetic analyses and molecular modeling show that one nearly full-length sequence from lamprey and two additional fragments include the entire integrin αI domain region, have the hallmarks of collagen-binding integrin αI domains, and we show that the corresponding recombinant proteins recognize the collagen GFOGER motifs in a metal dependent manner, unlike the α1I domain of the ascidian C. intestinalis. The presence of a functional collagen receptor integrin αI domain supports the origin of orthologues of the human integrins with αI domains prior to the earliest diverging extant vertebrates, a domain that has been conserved and diversified throughout the vertebrate lineage.
authors.affiliation: Structural Bioinformatics Laboratory, Biochemistry, Department of Biosciences, Åbo Akademi University, Turku, Finland.
authors.forename: Bhanupratap Singh
authors.initials: BS
authors.lastname: Chouhan
authors.affiliation: Department of Biochemistry, University of Turku, Turku, Finland.
authors.forename: Jarmo
authors.initials: J
authors.lastname: Käpylä
authors.affiliation: Structural Bioinformatics Laboratory, Biochemistry, Department of Biosciences, Åbo Akademi University, Turku, Finland.
authors.forename: Konstantin
authors.initials: K
authors.lastname: Denessiouk
authors.affiliation: Structural Bioinformatics Laboratory, Biochemistry, Department of Biosciences, Åbo Akademi University, Turku, Finland.
authors.forename: Alexander
authors.initials: A
authors.lastname: Denesyuk
authors.affiliation: Department of Biochemistry, University of Turku, Turku, Finland.
authors.forename: Jyrki
authors.initials: J
authors.lastname: Heino
authors.affiliation: Structural Bioinformatics Laboratory, Biochemistry, Department of Biosciences, Åbo Akademi University, Turku, Finland.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Johnson
mesh_terms: D000818:Animals; D019143:Evolution, Molecular; D006801:Humans; D039423:Integrin alpha1 / Q000737:chemistry* / Q000235:genetics*; D008958:Models, Molecular; D010802:Phylogeny; D017433:Protein Structure, Secondary; D014714:Vertebrates / Q000235:genetics* / Q000378:metabolism
chemical_list: D039423:Integrin alpha1