Structural highlights
Disease
C1QA_HUMAN Defects in C1QA are a cause of complement component C1q deficiency (C1QD) [MIM:613652. A rare defect resulting in C1 deficiency and impaired activation of the complement classical pathway. C1 deficiency generally leads to severe immune complex disease with features of systemic lupus erythematosus and glomerulonephritis.
Function
C1QA_HUMAN C1q associates with the proenzymes C1r and C1s to yield C1, the first component of the serum complement system. The collagen-like regions of C1q interact with the Ca(2+)-dependent C1r(2)C1s(2) proenzyme complex, and efficient activation of C1 takes place on interaction of the globular heads of C1q with the Fc regions of IgG or IgM antibody present in immune complexes.
Evolutionary Conservation
Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf.
Publication Abstract from PubMed
C1q, the recognition subunit of the C1 complex of complement, is an archetypal pattern recognition molecule with the striking ability to sense a wide variety of targets, including a number of altered self-motifs. The recognition properties of its globular domain were further deciphered by means of x-ray crystallography using deoxy-D-ribose and heparan sulfate as ligands. Highly specific recognition of deoxy-D-ribose, involving interactions with Arg C98, Arg C111, and Asn C113, was observed at 1.2 A resolution. Heparin-derived tetrasaccharide interacted more loosely through Lys C129, Tyr C155, and Trp C190. These data together with previous findings define a unique binding area exhibiting both polyanion and deoxy-D-ribose recognition properties, located on the inner face of C1q. DNA and heparin compete for C1q binding but are poor C1 activators compared with immune complexes. How the location of this binding area in C1q may regulate the level of C1 activation is discussed.
Cutting edge: C1q binds deoxyribose and heparan sulfate through neighboring sites of its recognition domain.,Garlatti V, Chouquet A, Lunardi T, Vives R, Paidassi H, Lortat-Jacob H, Thielens NM, Arlaud GJ, Gaboriaud C J Immunol. 2010 Jul 15;185(2):808-12. Epub 2010 Jun 14. PMID:20548024[1]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Garlatti V, Chouquet A, Lunardi T, Vives R, Paidassi H, Lortat-Jacob H, Thielens NM, Arlaud GJ, Gaboriaud C. Cutting edge: C1q binds deoxyribose and heparan sulfate through neighboring sites of its recognition domain. J Immunol. 2010 Jul 15;185(2):808-12. Epub 2010 Jun 14. PMID:20548024 doi:10.4049/jimmunol.1000184
