C1Q

Complement component C1q domain.
C1Q
SMART accession number:SM00110
Description: Globular domain found in many collagens and eponymously in complement C1q. When part of full length proteins these domains form a 'bouquet' due to the multimerization of heterotrimers. The C1q fold is similar to that of tumour necrosis factor.
Interpro abstract (IPR001073):

This entry represents the C-terminal domain of C1q. C1q is a subunit of the C1 enzyme complex that activates the serum complement system. C1q comprises 6 A, 6 B and 6 C chains. These share the same topology, each possessing a small, globular N-terminal domain, a collagen-like Gly/Pro-rich central region, and a conserved C-terminal region, the C1q domain [(PUBMED:1706597)]. The C1q protein is produced in collagen-producing cells and shows sequence and structural similarity to collagens VIII and X [(PUBMED:2591537), (PUBMED:2019595)]. This domain is also found in multimerin and EMILIN proteins.

The C-terminal globular domain of the C1q subcomponents and collagen types VIII and X is important both for the correct folding and alignment of the triple helix and for protein-protein recognition events [(PUBMED:1867713)]. For collagen type X it has been suggested that the domain is important for initiation and maintenance of the correct assembly of the protein [(PUBMED:1860888)]. The globular head is a trimer of C1q domains. Each individual C1q adopts a 10-strand Jelly-roll fold arranged in two antiparallel 5-stranded beta-sheets [(PUBMED:22892318)]. There are two well conserved regions within the C1q domain: an aromatic motif is located within the first half of the domain, the other conserved region is located near the C-terminal extremity.

Family alignment:
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There are 9593 C1Q domains in 9170 proteins in SMART's nrdb database.

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