Complement Component 1, q subcomponent (C1q) associates with C1r and C1s in order to yield the first component of the serum complement system. Deficiency of C1q has been associated with lupus erythematosus and glomerulonephritis. C1q is composed of 18 polypeptide chains: six A-chains, six B-chains, and six C-chains. Southern blot analysis of chromosomal DNA from vertebrate species demonstrated highest similarity between the C1qB genes, followed by C1qC and finally C1qA. Sequence comparison of C1q from three different species have shown that the B chains have the strongest similarity. C1q was already present at embryonic day 14 (E14) and showed little change in abundance through six weeks postnatal. At E16, C1qB mRNA was present at high abundance in putative microglia/macrophages in cortical marginal and intermediate zones, and hippocampal analge.
Complement Component 1Q Subcomponent-Binding Protein (C1QBP) is a nucleus protein that belongs to the MAM33 family. C1QBP is known to bind to the globular heads of C1q molecules and inhibit C1 activation. Mitochondrial C1QBP is a critical mediator of p14ARF-induced apoptosis. C1QBP functions as a chemotactic factor for immature dendritic cells, and migration is mediated through ligation of both C1QBP and cC1qR/CR. C1QBP overexpression successfully blocks mRNA accumulation from the adenovirus major late transcription unit (MLTU) and stimulates RNA polymerase II carboxy-terminal domain phosphorylation in virus-infected cells.
Hyaluronan binding protein 1 (HABP1), also known as p32 or gC1qR, is a ubiquitously expressed multifunctional phospho-protein implicated in cell signalling. Hyaluronan-binding protein 1 (HABP1) /p32/gC1qR was characterized as a highly acidic and oligomeric protein, which binds to different ligands like hyaluronan, C1q, and mannosylated albumin. The role of hyaluronan binding protein 1 (HABP1) in cell signaling was investigated and in vitro. HABP1 overexpressing cells showed extensive vacuolation and reduced growth rate, which was corrected by frequent medium replenishment. Further investigation revealed that HABP1 overexpressing cells undergo apoptosis, and they failed to enter into the S-phase. The sperm surface HABP1 level can be correlated with the degree of sperm motility.Hyaluronan binding protein 1 (HABP1) was reported to be present on human sperm surface and its involvement in fertilization has already been elucidated: decreased HABP1 level may be associated with low motility of sperms, which in turn might cause infertility in the patient. HABP1 also is an endogenous substrate for MAP kinase and upon mitogenic stimulation it is translocated to the nucleus in a MAP kinase-dependent manner.
C1QTNF1 is a secreted protein,contains 1 C1q domain and 1 collagen-like domain. C1qTNF proteins constitute a highly conserved family of Acrp30/Adiponectin paralogs that share a modular organization comprising an N-terminal signal peptide, a short variable region, a collagenous domain and a C-terminal globular domain. C1qTNF proteins are predicted to have trimeric structures that assemble into hexameric and higher order molecular forms. C1QTNF1 is a novel adipokine, providing a significant framework to further address the physiological functions and mechanisms of the action of this family of secreted glycoproteins in normal and disease states. C1QTNF1 increases the production of aldosterone. C1QTNF1 is vastly expressed in obese subjects as well as up-regulated in hypertensive patients, C1QTNF1 is identified molecular link between obesity and hypertension. C1QTNF1 expression may be associated with a low-grade chronic inflammation status in adipose tissues.
TISSUE SPECIFICITY: Expressed predominantly in adipose tissue. {ECO:0000269|PubMed:19666007}.
Complement component C2 is part of the classical complement pathway which plays a major role in innate immunity against infection. C2 is a glycoprotein synthesized in liver hepatocytes and several other cell types in extrahepatic tissues. This pathway is triggered by a multimolecular complex C1, and subsequently the single-chain form of C2 is cleaved into two chains referred to C2a and C2b by activated C1. The second component of complement (C2) is a multi-domain serine protease that provides catalytic activity for the C3 and C5 convertases of the classical and lectin pathways of human complement. C4b and C2 was investigated by surface plasmon resonance. C2a containing a serine protease domain combines with complement component C4b to form the C3 convertase C4b2a which is responsible for C3 activation, and leads to the stimulation of adaptive immune responses via Lectin pathway. C2 bound to C4b is cleaved by classical (C1s) or lectin (MASP2) proteases to produce C4bC2a. C2 has the same serine protease domain as C4bC2a but in an inactive zymogen-like conformation, requiring cofactor-induced conformational change for activity. Deficiency of C2 (C2D) is the most common genetic deficiency of the complement system, and two types of C2D have been recognized in the context of specific MHC haplotypes. C2D in human is reported to increase susceptibility to infection, and is associated with certain autoimmune diseases, such as rheumatological disorders.
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