Fibrous Proteins: Collagen and Elastin (Vocabulary)

Vocabulary flashcards covering collagen structure, types, biosynthesis, cross-linking, and elastin-related concepts from the lecture notes.

Fibrous proteins

Structural proteins that provide support and mechanical strength in tissues (e.g., collagen and elastin).

Collagen

Most abundant protein in the body; forms a rope-like triple helix of three α-chains.

α-chain (α1, α2)

One of the three polypeptide chains that compose collagen; chains assemble into the triple helix.

Triple helix

A rope-like structure formed by three collagen α-chains wound together.

Gly-X-Y sequence

Repeating collagen amino acid triplet where X is often proline and Y often hydroxyproline or hydroxylysine.

Glycine

The smallest amino acid; occurs every third residue in collagen to fit in the helix core.

Proline

Amino acid that introduces kinks in chains; prevents typical α-helix formation in collagen.

Hydroxyproline

Hydroxylated proline; stabilizes the collagen triple helix by enhancing interchain hydrogen bonds.

Hydroxylysine

Hydroxylated lysine; can be glycosylated and participates in cross-linking through lysyl residues.

Prolyl hydroxylase

Enzyme that hydroxylates proline residues in collagen precursors; requires vitamin C.

Lysyl hydroxylase

Enzyme that hydroxylates lysine residues in collagen; requires vitamin C.

Vitamin C (ascorbate)

Cofactor for prolyl and lysyl hydroxylases; deficiency impairs collagen maturation (scurvy).

Procollagen

Triple-helical collagen molecule with non-helical N- and C-terminal propeptides; secreted before processing.

Propeptides

N- and C-terminal extensions of procollagen that are removed extracellularly to form mature collagen.

Procollagen peptidases

Enzymes that cleave propeptides to release mature triple-helical collagen.

Tropocollagen

Basic collagen monomer after propeptide removal; assembles into fibrils.

Lysyl oxidase

Copper-containing enzyme that oxidatively deaminates lysine/hydroxylysine to aldehydes for cross-linking.

Cross-links

Covalent bonds (e.g., via allysine/hydroxyallysine) between collagen molecules; confer tensile strength.

Type I collagen

Fibril-forming in skin, bone, tendon; composed of two α1(I) and one α2(I) chains.

Type II collagen

Fibril-forming in cartilage; consists of three α1(II) chains.

Type III collagen

Fibril-forming in distensible tissues such as blood vessels.

Type IV collagen

Network-forming collagen that makes up basement membranes.

Type VII collagen

Network-forming collagen that anchors basement membranes to the dermis.

Fibril-associated collagens (IX, XII)

Collagens that bind to fibril surfaces, linking fibrils to other ECM components.

Collagenases

Proteolytic enzymes (matrix metalloproteinases) that degrade collagen fibrils.

Osteogenesis imperfecta

Brittle bone disease due to mutations in type I collagen; often glycine substitutions disrupt triple helix.

Ehlers-Danlos syndrome

Group of connective tissue disorders from defects in collagen types I/III/V or processing enzymes; hyperextensible skin, hypermobile joints.

Alport syndrome

Genetic disorder affecting type IV collagen; basement membranes of kidney, ear, and eye.

Epidermolysis bullosa

Skin fragility/blistering; dystrophic form involves COL7A1 (type VII collagen).

Elastin

Rubbery connective tissue protein; forms elastic fibers with microfibrils; stretch and recoil.

Tropoelastin

Soluble precursor to elastin; secreted and assembled into elastin in the ECM.

Fibrillin

Glycoprotein microfibrils scaffold for elastin deposition; mutations cause Marfan syndrome.

Desmosine cross-link

Unique cross-link in elastin formed by lysyl-derived residues; provides elasticity.

a1-antitrypsin (a1-AT)

Inhibitor of proteases such as neutrophil elastase; protects elastin in lungs; deficiency linked to emphysema.

Neutrophil elastase

Protease that degrades elastin in alveolar walls if not inhibited.

Emphysema

Lung disease caused by elastin degradation; accelerated in a1-AT deficiency and by smoking.

Williams-Beuren syndrome

Deletion of elastin gene on chromosome 7; supravalvular aortic stenosis and other features.

Scurvy

Vitamin C deficiency; impairs collagen hydroxylation and cross-linking, causing bruising and poor wound healing.

Glycosylation (collagen)

Glycosylation of hydroxylysine residues (glucose and galactose) before triple-helix formation.

Basement membrane

Sheet-like ECM structure formed largely by network-forming type IV collagen; semipermeable barrier.