Complement component 1q: Difference between revisions

Latest revision as of 18:59, 23 March 2025

Human protein involved in the complement system

Complement component 1q (C1q) is a protein complex involved in the complement system, which is part of the immune system. C1q is the first subcomponent of the C1 complex, which is the first component of the classical complement pathway. This pathway is one of the three pathways that activate the complement system, leading to a cascade of immune responses that help clear pathogens from an organism.

Structure[edit]

C1q is a large protein complex composed of 18 polypeptide chains, which form six heterotrimeric subunits. Each subunit consists of three different polypeptide chains: A, B, and C. These chains are arranged in a collagen-like triple helix structure. The C-terminal globular heads of C1q are responsible for binding to the Fc region of immunoglobulins, such as IgG and IgM, when they are bound to antigens.

Function[edit]

C1q plays a crucial role in the activation of the classical complement pathway. Upon binding to the Fc region of antibodies that are attached to antigens, C1q undergoes a conformational change that activates the C1r and C1s serine proteases. This activation leads to the cleavage of complement component 4 (C4) and complement component 2 (C2), forming the C4b2a complex, also known as the C3 convertase. The C3 convertase then cleaves complement component 3 (C3), leading to the opsonization of pathogens, recruitment of inflammatory cells, and eventual formation of the membrane attack complex.

Role in Disease[edit]

Deficiencies in C1q can lead to increased susceptibility to infections and are associated with autoimmune diseases such as systemic lupus erythematosus (SLE). C1q deficiency is a rare genetic disorder that results in impaired clearance of immune complexes and apoptotic cells, contributing to the development of autoimmunity.

Complement Pathway[edit]

The complement system consists of three pathways: the classical pathway, the lectin pathway, and the alternative pathway. C1q is specifically involved in the classical pathway, which is primarily activated by antigen-antibody complexes. The complement system plays a vital role in innate immunity, inflammation, and the clearance of immune complexes and apoptotic cells.

Related pages[edit]

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-'''Complement component 1q''' (C1q) is a protein complex that plays a crucial role in the [[immune system]], particularly in the classical pathway of the [[complement system]]. This system is a major part of the innate immune response, providing a rapid defense against pathogens. C1q is the first component of the complement system to act in the classical pathway, where it binds to antibodies that are attached to pathogens, initiating a series of reactions that lead to the destruction of the pathogen.
+{{Short description|Human protein involved in the complement system}}
+{{DISPLAYTITLE:Complement component 1q}}
-== Structure and Function ==
+[[File:PDB_1o91_EBI.jpg|Structure of Complement Component 1q|thumb|right]]
-C1q is a complex molecule made up of 18 polypeptide chains: six A-chains, six B-chains, and six C-chains. These chains are arranged in a bouquet-like structure, with a collagen-like region and a globular domain. The globular domain is responsible for recognizing and binding to the Fc region of antibodies (IgG and IgM) that are bound to antigens on the surface of pathogens.
-Upon binding to antibodies, C1q undergoes a conformational change that activates the C1r and C1s serine proteases, which are associated with C1q in the C1 complex. This activation leads to the sequential activation of other complement components, resulting in opsonization of pathogens, recruitment of inflammatory cells, and lysis of the pathogen's cell membrane through the formation of the membrane attack complex (MAC).
+'''Complement component 1q''' (C1q) is a protein complex involved in the [[complement system]], which is part of the [[immune system]]. C1q is the first subcomponent of the [[C1 complex]], which is the first component of the [[classical complement pathway]]. This pathway is one of the three pathways that activate the complement system, leading to a cascade of immune responses that help clear pathogens from an organism.
-== Role in Disease ==
+==Structure==
-While C1q is essential for the clearance of pathogens, dysregulation of the complement system can lead to various diseases. Deficiencies in C1q are associated with an increased susceptibility to infections and a higher risk of developing autoimmune diseases, such as systemic lupus erythematosus (SLE). In SLE, the absence or reduced levels of C1q can lead to impaired clearance of apoptotic cells and immune complexes, contributing to the autoimmune response.
+C1q is a large protein complex composed of 18 polypeptide chains, which form six heterotrimeric subunits. Each subunit consists of three different polypeptide chains: A, B, and C. These chains are arranged in a collagen-like triple helix structure. The C-terminal globular heads of C1q are responsible for binding to the [[Fc region]] of [[immunoglobulin]]s, such as [[IgG]] and [[IgM]], when they are bound to antigens.
-Moreover, excessive activation of C1q and the complement system can contribute to tissue damage in autoimmune and inflammatory diseases. In conditions such as rheumatoid arthritis, ischemia-reperfusion injury, and Alzheimer's disease, inappropriate activation of the complement system, including C1q, can exacerbate tissue inflammation and damage.
+==Function==
+C1q plays a crucial role in the activation of the classical complement pathway. Upon binding to the Fc region of antibodies that are attached to antigens, C1q undergoes a conformational change that activates the C1r and C1s serine proteases. This activation leads to the cleavage of [[complement component 4]] (C4) and [[complement component 2]] (C2), forming the C4b2a complex, also known as the [[C3 convertase]]. The C3 convertase then cleaves [[complement component 3]] (C3), leading to the opsonization of pathogens, recruitment of inflammatory cells, and eventual formation of the [[membrane attack complex]].
-== Clinical Significance ==
+==Role in Disease==
-The measurement of C1q levels and function can be used in the diagnosis and monitoring of diseases associated with complement system dysregulation. Therapeutic interventions targeting C1q and the complement system are being explored as potential treatments for autoimmune diseases, inflammatory conditions, and certain types of cancer, where complement activation plays a role in disease pathology.
+Deficiencies in C1q can lead to increased susceptibility to infections and are associated with autoimmune diseases such as [[systemic lupus erythematosus]] (SLE). C1q deficiency is a rare genetic disorder that results in impaired clearance of immune complexes and apoptotic cells, contributing to the development of autoimmunity.
-== Research Directions ==
+==Complement Pathway==
-Research on C1q is focused on understanding its role in the immune system and disease, developing therapies that can modulate its activity, and exploring its potential as a biomarker for disease. Studies are also investigating the role of C1q in neurodegenerative diseases, where it is involved in the clearance of amyloid-beta plaques, a hallmark of Alzheimer's disease.
+[[File:Complement_pathway.svg|Complement Pathway Diagram|thumb|left]]
+The complement system consists of three pathways: the classical pathway, the [[lectin pathway]], and the [[alternative pathway]]. C1q is specifically involved in the classical pathway, which is primarily activated by antigen-antibody complexes. The complement system plays a vital role in innate immunity, inflammation, and the clearance of immune complexes and apoptotic cells.
+==Related pages==
+* [[Complement system]]
+* [[Classical complement pathway]]
+* [[Immunoglobulin]]
+* [[Systemic lupus erythematosus]]
-[[Category:Immune system]]
 [[Category:Complement system]]
-{{Immunology-stub}}
+[[Category:Immunology]]
+[[Category:Proteins]]