collagen

Uses

• when partially hydrolyzed, the three tropocollagen strands separate into globular, random coils, producing gelatin

Function

• main protein of connective tissue in animals
• tough bundles of collagen (collagen fibers) are a major component of extracellular matrix
• great tensile strength
• along with soft keratin, give skin strength & elasticity
• collagen gives bone its elasticity & contributes to fracture resistance.
• strengthens blood vessels
• role in tissue development

Structure

• long, fibrous structural protein with triple helical structure, known as the Madras helix.
• tropocollagen or collage subunit is a rod about 300 nm long & 1.5 nm in diameter, made up of three polypeptide strands, each of which is a left-handed helix#
• the 3 left-handed helices are twisted together into a right-handed coiled-coil, stabilized by hydrogen bonds.
• tropocollagen subunits spontaneously self-assemble, with regularly staggered ends, into even larger arrays in the extracellular matrix of tissue
• some covalent crosslinking occurs within the triple helices
• variable amount of covalent crosslinking between tropocollagen helices
• tropocollagen from young animals can be extracted because it is not yet fully crosslinked
• a distinctive feature of collagen is the regular arrangement of amino acid residues in each of the 3 chains of collagen
• repeats of Gly-X-Pro or Gly-X-Hyp, where X may any amino acid residues
• in collagen, Gly is required at every 3rd position because the assembly of the triple helix puts this residue at the interior (axis) of the helix, where there is no space for a larger side group
• the rings of the Pro & Hyp must point outward
• Pro & Hyp thermally stabilize the triple helix, Hyp more so than Pro
• in bone, entire collagen triple helices lie in a parallel, staggered array
• 40 nm gaps between the ends of the tropocollagen subunits probably serve as nucleation sites for the deposition of long, hard, fine crystals of the mineral component, hydroxyapatite
• in this way that certain types of cartilage turn into bone
• collagen fibrils are collagen molecules packed into an organized overlapping bundle
• collagen fibers are bundles of fibrils.

# alpha helix is right-handed

Compartment

• extracellular matrix
• also found inside certain cells

Expression

• most abundant protein in mammals, comprises about 25% of total protein content
• 75% of the dry weight of skin tissue
• main component of fascia, cartilage, ligaments, tendons, bone & teeth
• present in the cornea & lens of the eye in crystalline form

formation of collagen:

• see collagen type-1

Pathology

• degradation leads to wrinkles that accompany skin aging
• scurvy is associated with defective collagen synthesis & weakened connective tissue
• in connective tissue diseases collagen fibers are destroyed with inflammation of surrounding tissues
• deposition of excess collagen occurs in scleroderma
• bacteria & viruses have virulence factors which destroy collagen or interfere with its production

Pharmacology

• used in cosmetic surgery & burns surgery

More general terms

• matrix protein
• multisubunit protein

More specific terms

• activated collagen
• collagen type-1
• collagen type-2
• collagen type-3
• collagen type-4
• collagen type-5
• collagen type-6
• collagen type-7
• collagen type-8 (endothelial collagen)
• collagen type-9 (FACIT collagen)
• collagen type-10
• collagen type-11
• collagen type-12
• collagen type-13

Additional terms

• collagenase