title: C1q and its growing family.
abstract: C1q is the target recognition protein of the classical complement pathway and a major connecting link between innate and acquired immunity. As a charge pattern recognition molecule of innate immunity, C1q can engage a broad range of self and non-self ligands via its heterotrimeric globular (gC1q) domain and thus trigger the classical pathway. The trimeric gC1q signature domain has been identified in a variety of non-complement proteins that can be grouped together as a C1q family. The X-ray crystal structures of the gC1q domain of a few members of the C1q family reveal a compact jelly-roll beta-sandwich fold similar to that of the multifunctional tumor necrosis factor (TNF) ligand family, hence the C1q and TNF superfamily. This review is an update on the structural and functional aspects of the gC1q domain of human C1q. We also mention the diverse range of proteins that utilize a gC1q domain in order to reflect on its importance as a versatile scaffold to support a variety of functions.
authors.affiliation: Institute of Medical Microbiology, Justus-Liebig-University, Frankfurter Strasse 107, 35392 Giessen, Germany.
authors.forename: Rohit
authors.initials: R
authors.lastname: Ghai
authors.forename: Patrick
authors.initials: P
authors.lastname: Waters
authors.forename: Lubka T
authors.initials: LT
authors.lastname: Roumenina
authors.forename: Mihaela
authors.initials: M
authors.lastname: Gadjeva
authors.forename: Mihaela S
authors.initials: MS
authors.lastname: Kojouharova
authors.forename: Kenneth B M
authors.initials: KB
authors.lastname: Reid
authors.forename: Robert B
authors.initials: RB
authors.lastname: Sim
authors.forename: Uday
authors.initials: U
authors.lastname: Kishore
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D015922:Complement C1q / Q000737:chemistry / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*; D019143:Evolution, Molecular; D016678:Genome / Q000235:genetics; D006801:Humans; D008024:Ligands; D010802:Phylogeny
chemical_list: D008024:Ligands; D015922:Complement C1q