title: The complete complement of C1q-domain-containing proteins in Homo sapiens.
abstract: The C-terminal domains of the A, B, C chains of C1q subcomponent of C1 complex represent a common structural motif, the C1q domain, that is found in a diverse range of proteins. We analyzed the human genome for the complete complement of this family and have identified a total of 31 independent gene sequences. The predominant organization of C1q-domain-containing (C1qDC) proteins includes a leading signal peptide, a collagen-like region of variable length, and a C-terminal C1q domain. There are 15 highly conserved residues within the C1q domain, among which 8 are invariant within the human gene set and these are predicted to cluster within the hydrophobic core of the protein. We suggest a 3-subfamily classification based on sequence homology. For some C1qDC-encoding genes, strict orthology has been retained throughout vertebrate evolution and these examples suggest a highly specific functional role for C1qDC proteins that has been under significant selective pressure. Alternatively, individual species have co-opted C1qDC proteins for roles that are highly specific to their biology, suggesting an evolutionary strategy of gene duplication and functional diversification. A more extensive analysis of the evolutionary relationship of C1qDC proteins reveals an ancient rooting, with clear members found in eubacterial species. Curiously, we have been unable to identify C1qDC-encoding genes in many eukaryotic genomcs, such as Sacchromyces cerivisae and C. elegans, suggesting that the retention or loss of this gene family throughout evolution has been sporadic.
authors.affiliation: Biology Research, Nuvelo, Sunnyvale, CA 94085, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Tom Tang
authors.forename: Tianhua
authors.initials: T
authors.lastname: Hu
authors.forename: Matthew
authors.initials: M
authors.lastname: Arterburn
authors.forename: Bryan
authors.initials: B
authors.lastname: Boyle
authors.forename: Jessica M
authors.initials: JM
authors.lastname: Bright
authors.forename: Servando
authors.initials: S
authors.lastname: Palencia
authors.forename: Peter C
authors.initials: PC
authors.lastname: Emtage
authors.forename: Walter D
authors.initials: WD
authors.lastname: Funk
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015922:Complement C1q / Q000737:chemistry / Q000235:genetics*; D030562:Databases, Protein; D019143:Evolution, Molecular; D014644:Genetic Variation; D015894:Genome, Human; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D011487:Protein Conformation; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D015922:Complement C1q