BI6.1-3 | Extracellular Matrix — Glossary

The complex network of proteins, polysaccharides, and water surrounding cells in tissues; provides structural support, regulates cell behaviour, and stores growth factors

The most abundant protein in the human body (~30% of total protein), characterised by a Gly-X-Y repeating sequence and a right-handed triple helix; provides tensile strength to tissues

The hallmark structure of collagen: three left-handed alpha-chains wound around each other into a right-handed supercoil, stabilised by interchain hydrogen bonds involving hydroxyproline

A modified amino acid formed by prolyl hydroxylase (requiring vitamin C, Fe2+, O2, alpha-ketoglutarate); essential for stabilising the collagen triple helix via hydrogen bonds

A modified amino acid formed by lysyl hydroxylase in the ER; serves as the attachment site for galactose and glucose in collagen glycosylation and participates in cross-linking

The intracellular precursor of collagen, containing N- and C-terminal propeptide extensions that prevent premature fibre assembly; secreted and then cleaved extracellularly

A copper-dependent extracellular enzyme that oxidises lysine and hydroxylysine residues in collagen and elastin to form covalent cross-links, providing mechanical strength

A genetic disorder of type I collagen (COL1A1/COL1A2 mutations) causing brittle bones, blue sclerae, dentinogenesis imperfecta, and hearing loss; also called brittle bone disease

A heterogeneous group of connective tissue disorders (13 types) caused by defects in collagen or collagen-processing enzymes, characterised by skin hyperextensibility and joint hypermobility

A disease caused by vitamin C deficiency leading to defective collagen hydroxylation; clinical features include bleeding gums, perifollicular haemorrhages, poor wound healing, and corkscrew hairs

An inherited disorder of type IV collagen (usually X-linked, COL4A5 mutation) affecting basement membranes; causes progressive nephritis, sensorineural deafness, and ocular abnormalities

A highly cross-linked, insoluble ECM protein that provides elastic recoil to tissues like arteries, lungs, and skin; cross-linked by desmosine and isodesmosine bridges

A glycoprotein that forms microfibrils scaffolding elastin deposition; mutations in the FBN1 gene cause Marfan syndrome (aortic dilatation, lens subluxation, tall stature)

A large adhesive glycoprotein dimer that connects cells to the ECM via integrin binding (RGD sequence); also binds collagen, fibrin, and heparin; important in wound healing and cell migration

A cross-shaped heterotrimer glycoprotein that is the major adhesive component of basement membranes; binds integrins, type IV collagen, and heparan sulphate proteoglycans

A transmembrane alpha-beta heterodimer receptor that links ECM proteins extracellularly to the actin cytoskeleton intracellularly; mediates cell adhesion, migration, and signal transduction

A long unbranched polysaccharide composed of repeating disaccharide units with dense negative charges that attract water, forming hydrated gels that resist compression

The only non-sulphated GAG; not attached to a core protein; forms very long chains in synovial fluid and vitreous humour; used clinically in intra-articular injections for osteoarthritis

The most highly sulphated GAG, found in mast cell granules; used clinically as an anticoagulant that activates antithrombin III to inhibit thrombin and Factor Xa

A macromolecule consisting of a core protein with covalently attached GAG chains (bottle-brush structure); aggrecan in cartilage is the prototypic example

The major proteoglycan of cartilage; binds hyaluronic acid via link proteins to form massive aggregates that resist compressive forces in joints

A group of lysosomal storage diseases caused by deficiency of enzymes that degrade GAGs, leading to progressive accumulation of undegraded GAG fragments in lysosomes

The most severe mucopolysaccharidosis caused by alpha-L-iduronidase deficiency; features coarse facies, corneal clouding, hepatosplenomegaly, and intellectual disability

The only X-linked mucopolysaccharidosis, caused by iduronate-2-sulphatase deficiency; similar to Hurler but without corneal clouding

A family of zinc-dependent endopeptidases that degrade ECM components; involved in wound healing, tissue remodelling, and pathologically in cancer invasion and arthritis