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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 [2] 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 [2] Genetics: - different alleles of the C4 gene produce different amounts of C4 protein [2]

Interactions

molecular events

Related

complement C4 in serum complement cascade

Specific

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

General

acute phase protein beta globulin complement glycoprotein

Properties

SIZE: MW = 193 kD entity length = 1744 aa COMPARTMENT: plasma MOTIF: N-glycosylation site {N226} cysteine residue {C702} MODIFICATION: cysteine residue {C728} cysteine residue {C703} MODIFICATION: cysteine residue {C735} cysteine residue {C716} MODIFICATION: cysteine residue {C736} cysteine residue {C728} MODIFICATION: cysteine residue {C702} cysteine residue {C735} MODIFICATION: cysteine residue {C703} cysteine residue {C736} MODIFICATION: cysteine residue {C716} N-glycosylation site {N862} N-glycosylation site {N1328} N-glycosylation site {N1391} sulfotyrosine site {Y1417} MODIFICATION: sulfate sulfotyrosine site {Y1420} MODIFICATION: sulfate sulfotyrosine site {Y1422} MODIFICATION: sulfate

Database Correlations

OMIM correlations UniProt P0C0L5

References

  1. Tietz Fundametals of Clinical Chemistry 3rd ed, WB Saunders, 1987 pg 327
  2. Sekar A et al. Schizophrenia risk from complex variation of complement component 4. Nature 2016 Jan 27 PMID: 26814963