Complement component 3

From Infogalactic: the planetary knowledge core
(Redirected from C3 (complement))
Jump to: navigation, search

<templatestyles src="Module:Infobox/styles.css"></templatestyles>

Complement component 3
250px
PDB rendering based on 1c3d.
Available structures
PDB Ortholog search: PDBe, RCSB
Identifiers
Symbols C3 ; AHUS5; ARMD9; ASP; C3a; C3b; CPAMD1; HEL-S-62p
External IDs OMIM120700 MGI88227 HomoloGene68031 ChEMBL: 4917 GeneCards: C3 Gene
EC number 3.4.21.43
Orthologs
Species Human Mouse
Entrez 718 12266
Ensembl ENSG00000125730 ENSMUSG00000024164
UniProt P01024 P01027
RefSeq (mRNA) NM_000064 NM_009778
RefSeq (protein) NP_000055 NP_033908
Location (UCSC) Chr 19:
6.68 – 6.73 Mb
Chr 17:
57.2 – 57.23 Mb
PubMed search [1] [2]

Complement component 3, often simply called C3, is a protein of the immune system. It plays a central role in the complement system and contributes to innate immunity. In humans it is encoded on chromosome 19 by a gene called C3.[1][2]

Function

C3 plays a central role in the activation of complement system.[3] Its activation is required for both classical and alternative complement activation pathways. People with C3 deficiency are susceptible to bacterial infection.[4][5]

One form of C3-convertase, also known as C4b2a, is formed by a heterodimer of activated forms of C4 and C2. It catalyzes the proteolytic cleavage of C3 into C3a and C3b, generated during activation through the classical pathway as well as the lectin pathway. C3a is an anaphylotoxin and the precursor of some cytokines such as ASP, and C3b serves as an opsonizing agent. Factor I can cleave C3b into C3c and C3d, the latter of which plays a role in enhancing B cell responses. In the alternative complement pathway, C3 is cleaved by C3bBb, another form of C3-convertase composed of activated forms of C3 (C3b) and factor B (Bb). Once C3 is activated to C3b, it exposes a reactive thioester that allows the peptide to covalently attach to any surface that can provide a nucleophile such as a primary amine or a hydroxyl group. Activated C3 can then interact with factor B. Factor B is then activated by factor D, to form Bb. The resultant complex, C3bBb, is called the alternative pathway (AP) C3 convertase.

C3bBb is deactivated in steps. First, the proteolytic component of the convertase, Bb, is removed by complement regulatory proteins having decay-accelerating factor (DAF) activity. Next, C3b is broken down progressively to first iC3b, then C3c + C3dg, and then finally C3d. Factor I is the protease that performs these cuts but it requires the help of another protein (Factor H, CR1, MCP or C4BP) to supply cofactor activity.

Structure

Several crystallographic structures of C3 have been determined[6] and reveal that this protein contains 13 domains.[7][8][9][10]

Clinical use

Complement tests
C4 (C) FB (A) C3 CH50 Conditions
 · PSG, C3 NeF AA
 ·  · HA, C4D
 ·  ·  · TCPD
 · /↓ SLE
inflammation

Levels of C3 in the blood may be measured to support or refute a particular medical diagnosis. For example, low C3 levels are associated with some types of kidney disease such as post-infectious glomerulonephritis, membranoproliferative glomerulonephritis, and shunt nephritis.

Interactions

Complement component 3 has been shown to interact with Factor H.[11][12]

References

  1. Lua error in package.lua at line 80: module 'strict' not found.
  2. Lua error in package.lua at line 80: module 'strict' not found.
  3. Lua error in package.lua at line 80: module 'strict' not found.
  4. Lua error in package.lua at line 80: module 'strict' not found.
  5. Lua error in package.lua at line 80: module 'strict' not found.
  6. Lua error in package.lua at line 80: module 'strict' not found.
  7. Lua error in package.lua at line 80: module 'strict' not found.
  8. Lua error in package.lua at line 80: module 'strict' not found.
  9. Lua error in package.lua at line 80: module 'strict' not found.
  10. Lua error in package.lua at line 80: module 'strict' not found.
  11. Lua error in package.lua at line 80: module 'strict' not found.
  12. Lua error in package.lua at line 80: module 'strict' not found.

Further reading

  • Lua error in package.lua at line 80: module 'strict' not found.

External links

This article incorporates text from the United States National Library of Medicine, which is in the public domain.