complement-4 (C4)

Function

• C4a is synthesized as a single-chain precursor
• prior to secretion, C4 is enzymatically cleaved to form a trimer of non-identical chains (alpha, beta, & gamma) linked by disulfide bonds
• activation of complement C4 by complement subcomponent C1s releases the C4a anaphylatoxin from the amino end of the alpha chain & generates C4b, which associates with the 2a fragment of complement factor 2 to form the classical-complement-pathway C3 convertase
• the C4b,C2a fragment then associates with the 3b fragment of complement factor 3 to form the classical-complement-pathway C5 convertase.
• C4a anaphylatoxin is a vasoactive peptide & a mediator of inflammation
• the activity of C4b is regulated by proteolytic cleavage involving C4b-binding protein & factor I

Compartment

• C4 protein is localized to synapses

Pathology

• brains of schizophrenic patients have excess production of C4
  • people with schizophrenia have fewer synapses than do people without schizophrenia
  • experiments in mice then showed that higher amounts of C4 lead to excess pruning of synapses

Genetics

• different alleles of the C4 gene produce different amounts of C4 protein

More general terms

• complement
• acute phase protein
• beta globulin
• glycoprotein

More specific terms

• complement C4a
• complement C4b
• complement C4d
• complement C4f (C4f)
• complement C4s (acidic complement C4)

Additional terms

• complement C4 in serum
• complement cascade

Database

• UniProt: http://www.uniprot.org/uniprot/P0C0L5.html
• OMIM: https://mirror.omim.org/entry/120790
• OMIM: https://mirror.omim.org/entry/120810
• OMIM: https://mirror.omim.org/entry/120820