COLLAGEN CHEMISTRY AND BIOLOGY DEFINITION: A protein with chains containing repetitive Gly-X-Y sequences allowing formation of molecules with triple-helical domains. The triple-helical domains as well as nontriple-helical domains of the molecules interact to form multimolecular aggregates that function primarily as structural elements in extracellular spaces. Collagens are the most abundant protein in mammals (25% of protein mass).

Locations of Collagens (Skin)

Locations of Collagens (Basement Membranes)

LOCATIONS OF COLLAGEN (VASCULAR SYSTEM)

LOCATIONS OF COLLAGENS BONES TEETH CARTILAGE

LOCATIONS OF COLLAGENS (TEETH)

LOCATIONS OF COLLAGENS (EYE) The lens capsule is a smooth, transparent basement membrane that completely surrounds the lens. The capsule is elastic and is composed of collagen.

Posterior Polymorphous Corneal Dystrophy One cause is a dominantly acting mutation in a gene encoding for collagen VIII (COL8A2). Ref: Coupal et al.

Osteogenesis imperfecta Blue sclerae of an OI victim Caused by genetic mutations in collagen genes COL1A1, COL1A2

COLLAGEN TYPES 27 types with 45genetically distinct chains: 1.Fiber-forming collagens: the quantitatively predominate collagens chains form several molecular species: (Types I, II, III, V, and XI) + (XXIV and XXVII) procollagen to collagen conversion fibers constructed of staggered, side to side, parallel association of molecules

COLLAGEN TYPES, CONT. 2. Fiber-associated collagens: (IX, XII, XIV, XVI, XIX, XX, XXI, XXII) 3. Network collagens (IV, VIII, X) 4. Filament collagen (VI) 5. Anchoring fibril collagen (VII) 6. Transmembrane collagens: (XIII, XVII, XXIII, XXV) 7. Multiplexins (XV, XVIII) Characteristics: 1) smaller and often numerous helical domains; 2) procollagen to collagen conversion (seldom); 3) staggered, side to side and antiparallel association when aggregates are formed.

Collagens: primary structure Almost every third residue is glycine Approx 17% is proline Contains hydroxyproline Contains hydroxylysine (which can form interchain bonds or be glycosylated)

Collagen – A Triple Helix Principal component of connective tissue (tendons, cartilage, bones, teeth) Basic unit is tropocollagen: Three intertwined polypeptide chains (1K residues each) MW = 285,000 300 nm long, 1.4 nm diameter Unique amino acid composition, including hydroxylysine and hydroxyproline Hydroxyproline is formed by the vitamin C-dependent prolyl hydroxylase reaction.

Collagen – Hydroxylation of Proline

Scurvy (Vitamin C deficiency) Scorbutic gums due to of scurvy. Notice gingival red triangles. Vitamin C is needed for post translational amino acid modifications in collagen.

Collagen – A Triple Helix The secrets of its a.a. composition... Nearly one residue out of three is Gly Proline content is unusually high Unusual amino acids found: 4-hydroxyproline 3-hydroxyproline 5-hydroxylysine Pro and HyPro together make 30% of res.

A case of structure following composition The Collagen Triple Helix A case of structure following composition The unusual amino acid composition of collagen is unsuited for alpha helices or beta sheets It is ideally suited for the collagen triple helix: three intertwined helical strands Much more extended than alpha helix, with a rise per residue of 2.9 Angstroms 3.3 residues per turn Long stretches of Gly-Pro-Pro/HyP

Collagen – A Triple Helix Figure 6.16 Poly(Gly-Pro-Pro), a collagen-like right-handed triple helix composed of three left-handed helical chains.

Staggered arrays of tropocollagens Collagen Fibers Staggered arrays of tropocollagens Banding pattern in EMs with 68 nm repeat Since tropocollagens are 300 nm long, there must be 40 nm gaps between adjacent tropocollagens (5 x 68 = 340 nm) 40 nm gaps are called "hole regions" - they contain carbohydrate and are thought to be nucleation sites for bone formation

Collagen – A Triple Helix Figure 6.17 In the electron microscope, collagen fibers exhibit alternating light and dark bands. The dark bands correspond to the 40-nm gaps between pairs of aligned collagen triple helices.

Pro and HyP suit the constraints of φ and ψ Structural basis of the collagen triple helix Every third residue faces the crowded center of the helix - only Gly fits here Pro and HyP suit the constraints of φ and ψ Interchain H-bonds involving HyP stabilize helix Fibrils are further strengthened by intrachain lysine-lysine and interchain hydroxypyridinium crosslinks

The hole regions of collagen fibrils may be the sites of nucleation for bone mineralization A disaccharide of galactose and glucose is covalently linked to the 5-hydroxyl group of hydroxylysines in collagen by the combined action of galactosyltransferase and glucosyltransferase.

LYSYL HYDROXYLATION

MINERALIZATION

SYNTHESIS – ASSEMBLY OF A COLLAGEN MOLECULE

SPECIFICITY OF CHAIN ASSOCIATION

EXTRACELLLULAR PROCESSING OF COLLAGEN

FIBER ARCHITECTURE

CROSS-LINKS IN A FIBER PHYSICAL STABILITY

FIBROUS COLLAGEN SUMMARY

INDUSTRIAL AND CLINICAL USES OF COLLAGEN Denatured collagen (gelatin): FOODS COATINGS CAPSULES Native collagen: SURGICAL DRESSINGS IMPLANTS TISSUE ENGINEERING

PREPARATION FOR CROSS-LINKING

REACTIONS FOR CROSS-LINKS