UniProt functional annotation for P0C0L4



	UniProt functional annotation for P0C0L4

UniProt code: P0C0L4.

Organism: Homo sapiens (Human).

Taxonomy: Eukaryota; Metazoa; Chordata; Craniata; Vertebrata; Euteleostomi; Mammalia; Eutheria; Euarchontoglires; Primates; Haplorrhini; Catarrhini; Hominidae; Homo.

Function: Non-enzymatic component of C3 and C5 convertases and thus essential for the propagation of the classical complement pathway. Covalently binds to immunoglobulins and immune complexes and enhances the solubilization of immune aggregates and the clearance of IC through CR1 on erythrocytes. C4A isotype is responsible for effective binding to form amide bonds with immune aggregates or protein antigens, while C4B isotype catalyzes the transacylation of the thioester carbonyl group to form ester bonds with carbohydrate antigens.

Function: Derived from proteolytic degradation of complement C4, C4a anaphylatoxin is a mediator of local inflammatory process. It induces the contraction of smooth muscle, increases vascular permeability and causes histamine release from mast cells and basophilic leukocytes.

Subunit: Circulates in blood as a disulfide-linked trimer of an alpha, beta and gamma chain.

Subcellular location: Secreted. Cell junction, synapse {ECO:0000269|PubMed:26814963}. Cell projection, axon {ECO:0000269|PubMed:26814963}. Cell projection, dendrite {ECO:0000269|PubMed:26814963}.

Tissue specificity: Complement component C4 is expressed at highest levels in the liver, at moderate levels in the adrenal cortex, adrenal medulla, thyroid gland, and the kidney, and at lowest levels in the heart, ovary, small intestine, thymus, pancreas and spleen. The extra- hepatic sites of expression may be important for the local protection and inflammatory response. {ECO:0000269|PubMed:11367523}.

Ptm: Prior to secretion, the single-chain precursor is enzymatically cleaved to yield non-identical chains alpha, beta and gamma. During activation, the alpha chain is cleaved by C1 into C4a and C4b, and C4b stays linked to the beta and gamma chains. Further degradation of C4b by C1 into the inactive fragments C4c and C4d blocks the generation of C3 convertase. The proteolytic cleavages often are incomplete so that many structural forms can be found in plasma.

Ptm: N- and O-glycosylated. O-glycosylated with a core 1 or possibly core 8 glycan. {ECO:0000269|PubMed:12754519, ECO:0000269|PubMed:14760718, ECO:0000269|PubMed:16335952, ECO:0000269|PubMed:18780401, ECO:0000269|PubMed:19139490, ECO:0000269|PubMed:19159218, ECO:0000269|PubMed:19838169, ECO:0000269|PubMed:23234360}.

Polymorphism: The complement component C4 is the most polymorphic protein of the complement system. It is the product of 2 closely linked and highly homologous genes, C4A and C4B. Once polymorphic variation is discounted, the 2 isotypes differ by only 4 amino acids at positions 1120-1125: PCPVLD for C4A and LSPVIH for C4B. The 2 isotypes bear several antigenic determinants defining Chido/Rodgers blood group system [MIM:614374]. Rodgers determinants are generally associated with C4A allotypes, and Chido with C4B. Variations at these loci involve not only nucleotide polymorphisms, but also gene number and gene size. Some individuals may lack either C4A, or C4B gene. Partial deficiency of C4A or C4B is the most commonly inherited immune deficiency known in humans with a combined frequency over 31% in the normal Caucasian population (PubMed:11367523). C4A6 allotype is deficient in hemolytic activity. Allotype C4A13 is infrequent. Common copy-number variants of C4A and C4B affecting expression of complement component C4 in the brain have been associated with schizophrenia risk (PubMed:26814963). {ECO:0000269|PubMed:11367523, ECO:0000269|PubMed:26814963}.

Disease: Complement component 4A deficiency (C4AD) [MIM:614380]: A rare defect of the complement classical pathway associated with the development of autoimmune disorders, mainly systemic lupus with or without associated glomerulonephritis. {ECO:0000269|PubMed:8473511}. Note=The disease is caused by variants affecting the gene represented in this entry.

Disease: Systemic lupus erythematosus (SLE) [MIM:152700]: A chronic, relapsing, inflammatory, and often febrile multisystemic disorder of connective tissue, characterized principally by involvement of the skin, joints, kidneys and serosal membranes. It is of unknown etiology, but is thought to represent a failure of the regulatory mechanisms of the autoimmune system. The disease is marked by a wide range of system dysfunctions, an elevated erythrocyte sedimentation rate, and the formation of LE cells in the blood or bone marrow. {ECO:0000269|PubMed:10092831, ECO:0000269|PubMed:17503323}. Note=Disease susceptibility is associated with variants affecting the gene represented in this entry. Interindividual copy-number variation (CNV) of complement component C4 and associated polymorphisms result in different susceptibilities to SLE. The risk of SLE susceptibility has been shown to be significantly increased among subjects with only two copies of total C4. A high copy number is a protective factor against SLE.

Sequence caution: Sequence=AAB59537.1; Type=Miscellaneous discrepancy; Note=During cDNA synthesis, the 5' end has been inverted (PubMed:3838531).; Evidence={ECO:0000305|PubMed:3838531}; Sequence=BAE06071.1; Type=Erroneous initiation; Note=Extended N-terminus.; Evidence={ECO:0000305};

Annotations taken from UniProtKB at the EBI.


Organism:		Homo sapiens (Human).
Taxonomy:		Eukaryota; Metazoa; Chordata; Craniata; Vertebrata; Euteleostomi; Mammalia; Eutheria; Euarchontoglires; Primates; Haplorrhini; Catarrhini; Hominidae; Homo.



Function:		Non-enzymatic component of C3 and C5 convertases and thus essential for the propagation of the classical complement pathway. Covalently binds to immunoglobulins and immune complexes and enhances the solubilization of immune aggregates and the clearance of IC through CR1 on erythrocytes. C4A isotype is responsible for effective binding to form amide bonds with immune aggregates or protein antigens, while C4B isotype catalyzes the transacylation of the thioester carbonyl group to form ester bonds with carbohydrate antigens.



Function:		Derived from proteolytic degradation of complement C4, C4a anaphylatoxin is a mediator of local inflammatory process. It induces the contraction of smooth muscle, increases vascular permeability and causes histamine release from mast cells and basophilic leukocytes.


Subunit:		Circulates in blood as a disulfide-linked trimer of an alpha, beta and gamma chain.
Subcellular location:		Secreted. Cell junction, synapse {ECO:0000269\|PubMed:26814963}. Cell projection, axon {ECO:0000269\|PubMed:26814963}. Cell projection, dendrite {ECO:0000269\|PubMed:26814963}.
Tissue specificity:		Complement component C4 is expressed at highest levels in the liver, at moderate levels in the adrenal cortex, adrenal medulla, thyroid gland, and the kidney, and at lowest levels in the heart, ovary, small intestine, thymus, pancreas and spleen. The extra- hepatic sites of expression may be important for the local protection and inflammatory response. {ECO:0000269\|PubMed:11367523}.
Ptm:		Prior to secretion, the single-chain precursor is enzymatically cleaved to yield non-identical chains alpha, beta and gamma. During activation, the alpha chain is cleaved by C1 into C4a and C4b, and C4b stays linked to the beta and gamma chains. Further degradation of C4b by C1 into the inactive fragments C4c and C4d blocks the generation of C3 convertase. The proteolytic cleavages often are incomplete so that many structural forms can be found in plasma.
Ptm:		N- and O-glycosylated. O-glycosylated with a core 1 or possibly core 8 glycan. {ECO:0000269\|PubMed:12754519, ECO:0000269\|PubMed:14760718, ECO:0000269\|PubMed:16335952, ECO:0000269\|PubMed:18780401, ECO:0000269\|PubMed:19139490, ECO:0000269\|PubMed:19159218, ECO:0000269\|PubMed:19838169, ECO:0000269\|PubMed:23234360}.
Polymorphism:		The complement component C4 is the most polymorphic protein of the complement system. It is the product of 2 closely linked and highly homologous genes, C4A and C4B. Once polymorphic variation is discounted, the 2 isotypes differ by only 4 amino acids at positions 1120-1125: PCPVLD for C4A and LSPVIH for C4B. The 2 isotypes bear several antigenic determinants defining Chido/Rodgers blood group system [MIM:614374]. Rodgers determinants are generally associated with C4A allotypes, and Chido with C4B. Variations at these loci involve not only nucleotide polymorphisms, but also gene number and gene size. Some individuals may lack either C4A, or C4B gene. Partial deficiency of C4A or C4B is the most commonly inherited immune deficiency known in humans with a combined frequency over 31% in the normal Caucasian population (PubMed:11367523). C4A6 allotype is deficient in hemolytic activity. Allotype C4A13 is infrequent. Common copy-number variants of C4A and C4B affecting expression of complement component C4 in the brain have been associated with schizophrenia risk (PubMed:26814963). {ECO:0000269\|PubMed:11367523, ECO:0000269\|PubMed:26814963}.
Disease:		Complement component 4A deficiency (C4AD) [MIM:614380]: A rare defect of the complement classical pathway associated with the development of autoimmune disorders, mainly systemic lupus with or without associated glomerulonephritis. {ECO:0000269\|PubMed:8473511}. Note=The disease is caused by variants affecting the gene represented in this entry.
Disease:		Systemic lupus erythematosus (SLE) [MIM:152700]: A chronic, relapsing, inflammatory, and often febrile multisystemic disorder of connective tissue, characterized principally by involvement of the skin, joints, kidneys and serosal membranes. It is of unknown etiology, but is thought to represent a failure of the regulatory mechanisms of the autoimmune system. The disease is marked by a wide range of system dysfunctions, an elevated erythrocyte sedimentation rate, and the formation of LE cells in the blood or bone marrow. {ECO:0000269\|PubMed:10092831, ECO:0000269\|PubMed:17503323}. Note=Disease susceptibility is associated with variants affecting the gene represented in this entry. Interindividual copy-number variation (CNV) of complement component C4 and associated polymorphisms result in different susceptibilities to SLE. The risk of SLE susceptibility has been shown to be significantly increased among subjects with only two copies of total C4. A high copy number is a protective factor against SLE.
Sequence caution:		Sequence=AAB59537.1; Type=Miscellaneous discrepancy; Note=During cDNA synthesis, the 5' end has been inverted (PubMed:3838531).; Evidence={ECO:0000305\|PubMed:3838531}; Sequence=BAE06071.1; Type=Erroneous initiation; Note=Extended N-terminus.; Evidence={ECO:0000305};