Complement Component C1Q

Complement Component C1Q (Proteins | Antibodies | Genes | ELISA Kits)

More Complement Component C1

Complement Component C1Q Background

The classical pathway plays a role in both innate and adaptive immunity.C1q family proteins are characterized by a distinctive 'globular domain' of about 140 amino acids (the gC1q domain) situated at the carboxyl terminus of a collagen 'stalk'. They often form a characteristic superstructure in which three protomers trimerize to form a collagen triple helix, and these trimers multimerize to form a ‘bouquet’. Complement component C1q, the first component of this pathway, links the adaptive humoral immune response to the complement system by binding to antibodies complexed with antigens. C1q can, however, also bind directly to the surface of certain pathogens and thus trigger complement activation in the absence of antibody. C1q is part of the C1 complex, which comprises a single C1q molecule bound to two molecules each of the zymogens C1r and C1s. Complement component C1q is a calcium-dependent sugar-binding protein, a lectin, belonging to the collectin family of proteins, which contains both collagen-like and lectin domains hence the name collectin. It has six globular heads, linked together by a collagen-like tail, which surround the (C1r:C1s)2 complex. Binding of more than one of the C1q heads to a pathogen surface causes a conformational change in the (C1r:C1s)2 complex, which leads to activation of an autocatalytic enzymatic activity in C1r; the active form of C1r then cleaves its associated C1s to generate an active serine protease.

Complement Component C1Q Reference

1. Janeway Jr C A, et al. (2001). The complement system and innate immunity.
2. Shapiro L, et al. (1998). The crystal structure of a complement-1q family protein suggests an evolutionary link to tumor necrosis factor. Current Biology, 8(6), 335-340.
3. Reid K B, et al. (1989). Structure-function relationships of the complement components. Immunology today, 10(6), 177-180.

Complement System
Complement System Overview
Complement System Component / Protein Regulator and Receptor
Complement Component / Protein of Complement System+
- Complement Component C1
Complement Component C1R
Complement Component C1S
Complement Component C1Q
Complement Component C1Q: C1QA
Complement Component C1Q: C1QB
Complement Component C1Q: C1QBP
Complement Component C1Q: C1QC
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- Complement Component C5
- Complement Component C6
- Complement Component C7
- Complement Component C8
- Complement Component C9
- Complement Component Factor B/CFB
- Complement Component Factor D/CFD/Adipsin
- Complement Component Factor Properdin/CFP
Complement Genetic Feature
Complement Activation Pathways
Complement System Role
Complement System and Diseases
Complement System Deficiency Diseases
Complement System Structure
Complement System Effector Functions
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