Collagen
The most abundant protein in the human body, providing structural strength to skin, tendons, ligaments, bones, and connective tissues. At least 28 types exist, with types I (skin/tendons/bones), II (cartilage), and III (skin/blood vessels) being most abundant. Collagen production declines with age.
Technical Context
Collagen superfamily: 28 types identified, classified as fibrillar (I, II, III, V, XI — forming rope-like structures), network-forming (IV — basement membranes), fibril-associated (IX, XII, XIV — linking fibrils), anchoring (VII — anchoring basement membrane to underlying tissue), transmembrane (XIII, XVII, XXIII, XXV), and others. Type I collagen: most abundant, forms thick fibres with high tensile strength, predominant in skin (80%), tendons (85%), bone (90%), and ligaments. Triple helix structure: three alpha chains with characteristic Gly-X-Y repeats (where X is often proline, Y is often hydroxyproline) wind around each other in a left-handed helix. Collagen degradation: matrix metalloproteinases (MMPs) — collagenases (MMP-1, MMP-8, MMP-13) make a single cut in the triple helix, followed by gelatinases (MMP-2, MMP-9) degrading the resulting fragments. Collagen turnover in skin: approximately 5-10% per year in adults, declining with age.