Complement component 1q
The complement component 1q (or simply C1q) is a protein complex involved in the complement system, which is part of the innate immune system.
C1q together with C1r and C1s form the C1 complex.
Antibodies of the adaptive immune system can bind antigen, forming an antigen-antibody complex.
C1q is primarily involved in the activation of the classical complement pathway by binding to the Fc regions of immunoglobulins (IgG or IgM) that are complexed with antigens.
This binding triggers a cascade of proteolytic activations involving C1r and C1s, leading to the formation of the C3 convertase and subsequent complement activation.
C1q has several non-complement functions: involved in the clearance of apoptotic cells and immune complexes, thereby preventing autoimmunity.
C1q also modulates various cellular processes, including phagocytosis, cytokine production, and T-lymphocyte maturation.
C1q has been implicated in tissue repair, pregnancy, cancer, and neuronal network regulation within the central nervous system.
When C1q binds antigen-antibody complexes, the C1 complex becomes activated.
Activation of the C1 complex initiates the classical complement pathway of the complement system.
The antibodies IgM and all IgG subclasses except IgG4 are able to initiate the complement system.
C1q is a multifunctional glycoprotein is subcomponent of the classical complement pathway. that plays a critical role in the immune system.
It is composed of 18 polypeptide chains organized into six heterotrimeric subunits, each containing three different types of chains (A, B, and C).
These subunits form a hexameric structure with six collagen-like triple helices terminating in globular head regions.
C1q is primarily involved in the activation of the classical complement pathway by binding to the Fc regions of immunoglobulins (IgG or IgM) that are complexed with antigens.
This binding triggers a cascade of proteolytic activations involving C1r and C1s, leading to the formation of the C3 convertase and subsequent complement activation.
C1q has several non-complement functions: clearance of apoptotic cells and immune complexes, thereby preventing autoimmunity.
C1q also modulates various cellular processes, including phagocytosis, cytokine production, and T-lymphocyte maturation.
C1q has been implicated in tissue repair, pregnancy, cancer, and neuronal network regulation within the central nervous system.
C1q is a versatile molecule with both complement-dependent and independent roles, crucial for immune regulation and maintaining homeostasis.
C1q is a 460 kDa protein formed from 18 peptide chains in 3 subunits of 6.
Each 6 peptide subunit consists of a Y-shaped pair of triple peptide helices joined at the stem and ending in a globular non-helical head.
C1q is composed of 18 polypeptide chains: six A-chains, six B-chains, and six C-chains.
The C1q domain is a conserved protein domain, and is a subunit of the C1 enzyme complex that activates the serum complement system. C1q comprises 6 A, 6 B and 6 C chains.
The C1q protein is produced in collagen-producing cells and shows sequence and structural similarity to collagens VIII and X.
The globular ends are the sites for multivalent attachment to the complement fixing sites in immune complexed immunoglobulin.
Patients with Lupus erythematosus often have deficient expression of C1q.
Genetic deficiency of C1q is extremely rare, with approximately 75 known cases, and the majority (>90%) of those have SLE.
C1q associates with C1r and C1s in order to yield the C1 complex (C1qr2s2), the first component of the serum complement system.
Deficiency of C1q has been associated with lupus erythematosus and glomerulonephritis.
It is potentially multivalent for attachment to the complement fixation sites of immunoglobulin.
IgG4 cannot bind C1q, but the other three IgG subclasses can.