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title: Collagen IV Alpha-2 Chain Protein
Collagen IV Alpha-2 Chain
<div class="infobox infobox-protein"> [@kuo2012]
| Property | Value | [@rannikmae2017] |----------|-------| [@verbeek2012] | Protein Name | Collagen type IV alpha-2 chain | [@nyitrai2007] | Aliases | COL4A2, Collagen IV α2 | [@joutel2010] | Gene | [COL4A2](/genes/col4a2) | | UniProt ID | [P08572](https://www.uniprot.org/uniprot/P08572) | | PDB IDs | [1LI1](https://www.rcsb.org/structure/1LI1) (collagen IV NC1 domain) | | Molecular Weight | ~168 kDa (precursor) | | Amino Acids | 1,712 | | Protein Family | Collagen superfamily, type IV (network-forming) | | Subcellular Localization | Extracellular matrix (basement membrane) | | Post-translational Modifications | Signal peptide cleavage, proline/lysine hydroxylation, glycosylation, NC1 domain cross-linking |
</div>
Overview
Collagen type IV alpha-2 chain is a protein encoded by the [COL4A2](/genes/col4a2) gene. This page describes its structure, normal nervous system function, role in neurodegenerative disease, and potential as a therapeutic target.
Structure
Collagen IV α2 is a large structural protein with the characteristic collagen triple-helical organization. It assembles with two [Collagen IV α1](/proteins/col4a1-protein) chains to form the α1α1α2(IV) protomer, the predominant type IV collagen isoform in most basement membranes including the cerebrovascular basement membrane.
Domain Architecture
...
title: Collagen IV Alpha-2 Chain Protein
Collagen IV Alpha-2 Chain
<div class="infobox infobox-protein"> [@kuo2012]
| Property | Value | [@rannikmae2017] |----------|-------| [@verbeek2012] | Protein Name | Collagen type IV alpha-2 chain | [@nyitrai2007] | Aliases | COL4A2, Collagen IV α2 | [@joutel2010] | Gene | [COL4A2](/genes/col4a2) | | UniProt ID | [P08572](https://www.uniprot.org/uniprot/P08572) | | PDB IDs | [1LI1](https://www.rcsb.org/structure/1LI1) (collagen IV NC1 domain) | | Molecular Weight | ~168 kDa (precursor) | | Amino Acids | 1,712 | | Protein Family | Collagen superfamily, type IV (network-forming) | | Subcellular Localization | Extracellular matrix (basement membrane) | | Post-translational Modifications | Signal peptide cleavage, proline/lysine hydroxylation, glycosylation, NC1 domain cross-linking |
</div>
Overview
Collagen type IV alpha-2 chain is a protein encoded by the [COL4A2](/genes/col4a2) gene. This page describes its structure, normal nervous system function, role in neurodegenerative disease, and potential as a therapeutic target.
Structure
Collagen IV α2 is a large structural protein with the characteristic collagen triple-helical organization. It assembles with two [Collagen IV α1](/proteins/col4a1-protein) chains to form the α1α1α2(IV) protomer, the predominant type IV collagen isoform in most basement membranes including the cerebrovascular basement membrane.
Domain Architecture
Signal peptide (aa 1-27) — Directs the nascent chain to the endoplasmic reticulum for secretion
7S domain (aa 28-174) — N-terminal domain that mediates lateral association of four protomers into antiparallel tetramers stabilized by disulfide bonds and lysyl oxidase-mediated cross-links
Triple-helical collagenous domain (aa 175-1,433) — The major structural region; composed of ~1,260 amino acids with the characteristic Gly-X-Y repeat. Contains ~22 interruptions in the Gly-X-Y repeat that introduce flexibility and serve as binding sites for cell surface receptors (integrins), proteases (MMPs), and other ECM components
NC1 (Non-Collagenous 1) domain (aa 1,434-1,712) — C-terminal globular domain that initiates chain selection and trimerization; mediates NC1-NC1 dimerization of protomers to form the characteristic collagen IV network; contains a sulfilimine bond (Met-Hyl cross-link) catalyzed by peroxidasin
Assembly and Network Formation
Collagen IV network assembly follows a hierarchical pathway:
Chain selection and trimerization — NC1 domains of two α1(IV) and one α2(IV) chains associate in the ER, nucleating triple helix formation that zips from C- to N-terminus
Proline hydroxylation — [Prolyl-4-hydroxylase](/proteins/p4ha1-protein) hydroxylates proline residues to hydroxyproline, stabilizing the triple helix at body temperature
Lysine hydroxylation and glycosylation — [Lysyl hydroxylase](/proteins/plod1-protein) modifies specific lysine residues; galactose and glucose are added
Secretion — The procollagen protomer is secreted via large COPII vesicles (requires [TANGO1](/proteins/mia3-protein) and HSP47 chaperone)
7S tetramerization — Four protomers associate at their N-terminal 7S domains, forming antiparallel tetramers
NC1 dimerization — C-terminal NC1 hexamers (two trimers) form end-to-end dimers via sulfilimine bonds catalyzed by [peroxidasin](/proteins/pxdn-protein)
Lateral interactions — Protomers associate side-to-side via the triple-helical domain, forming a sheet-like network
Gly-X-Y Repeat and Disease Mutations
The Gly-X-Y repeat in the collagenous domain requires glycine at every third position because only glycine is small enough to fit in the interior of the triple helix. Mutations replacing glycine with bulkier amino acids (Gly→Arg, Gly→Asp, Gly→Glu) destabilize the triple helix and are the most common cause of COL4A2-related disease.
Function in the Neurovascular Unit
Blood-Brain Barrier (BBB)
Collagen IV α1α1α2 is the primary structural component of the cerebrovascular basement membrane and is essential for [BBB](/entities/blood-brain-barrier) integrity:
Endothelial support — Provides the substrate for [endothelial cell](/cell-types/endothelial-cells) adhesion via α1β1 and α2β1 integrin receptors
Pericyte anchoring — [Pericytes](/cell-types/pericytes) attach to the basement membrane via integrin and dystroglycan complexes; collagen IV is the primary anchoring substrate
Astrocyte endfoot attachment — [Astrocyte](/cell-types/astrocytes) endfeet contact the abluminal basement membrane through [dystroglycan](/proteins/dag1-protein) and aquaporin-4 complexes
Selective permeability — The collagen IV network acts as a charge- and size-selective filter, restricting passage of plasma proteins
Growth factor reservoir — Binds and presents VEGF, PDGF-BB, and FGF-2 to regulate angiogenesis and vessel stability
Perivascular Drainage
The basement membrane serves as the conduit for perivascular (glymphatic) clearance of interstitial solutes including [amyloid-beta](/proteins/amyloid-beta):
Interstitial fluid drains along perivascular basement membranes in the reverse direction of blood flow
Collagen IV provides the structural channel for this drainage
Basement membrane thickening or disruption (as in COL4A2 mutations, aging, or hypertension) impairs drainage
Impaired perivascular drainage promotes Aβ accumulation in vessel walls, leading to [cerebral amyloid angiopathy (CAA)](/diseases/cerebral-amyloid-angiopathy)
Role in Neurodegeneration
Cerebral Small Vessel Disease (CSVD)
COL4A2 protein dysfunction causes progressive CSVD through:
ER retention of misfolded procollagen — Glycine substitution mutations prevent proper triple helix folding; misfolded protomers accumulate in the ER, triggering the [unfolded protein response (UPR)](/mechanisms/endoplasmic-reticulum-stress)))))))))))))))))))
Reduced basement membrane deposition — Both the mutant and wild-type chains are retained in the ER (dominant-negative effect), reducing overall collagen IV in the basement membrane
Basement membrane thinning — Reduced collagen IV weakens the structural integrity of cerebrovascular basement membranes
Vessel wall fragility — Weakened vessels are prone to dilation, microaneurysm formation, and rupture (hemorrhage)
BBB breakdown — Compromised basement membrane allows plasma protein leakage, driving perivascular inflammation and white matter damage
Vascular Contributions to Neurodegeneration
Chronic COL4A2-related vascular dysfunction contributes to neurodegeneration through:
Chronic hypoperfusion — Small vessel disease reduces cerebral blood flow, causing chronic ischemia that damages white matter and promotes neuronal loss
Neuroinflammation — BBB leakage admits plasma proteins (fibrinogen, thrombin, albumin) that activate [microglia](/cell-types/microglia) and drive inflammatory cascades
[Jeanne et al., COL4A2 mutations impair COL4A1 and COL4A2 secretion and cause hemorrhagic stroke (2012) (2012)](https://doi.org/10.1016/j.ajhg.2012.09.002)
[Khoshnoodi et al., Mammalian collagen IV (2008) (2008)](https://doi.org/10.1016/j.mam.2007.11.001)
[Poschl et al., Collagen IV is essential for basement membrane stability but dispensable for initiation of its assembly during early development (2004) (2004)](https://doi.org/10.1242/dev.01072)
[Kuo et al., Collagen IV mutation causes cerebrovascular disease and BBB defects (2012) (2012)](https://doi.org/10.1093/hmg/dds225)
[Rannikmae et al., COL4A2 is associated with lacunar ischaemic stroke and deep ICH (2017) (2017)](https://doi.org/10.1212/WNL.0000000000003659)
[Verbeek et al., COL4A2 mutation associated with familial porencephaly and small-vessel disease (2012) (2012)](https://doi.org/10.1038/ejhg.2012.49)
[Nyitrai et al., Canstatin inhibits tube formation and invasion of endothelial cells by binding to integrin αvβ3 and αvβ5 (2007) (2007)](https://doi.org/10.1016/j.bbrc.2404.09.138)
[Joutel et al., Cerebrovascular dysfunction and microcirculation rarefaction precede white matter lesions (2010) (2010)](https://doi.org/10.1172/JCI39799)