Collagen by Kati Feken

Crystal structure of collagen which has three identical helices shown in blue, green, and purple. Each helix consists of 18 residues.

View down central axis of same collagen structure.

Sequence of each helix: XGPXGPXGPX GPRGQXGV with X=any amino acid

*Structures made using Rasmol and pdb file 2WUH

Structure

• Composed of three identical, left-handed helices

• 3 amino acids per turn• Sequence: Gly-X-Y • Predominantly X=proline,

Y=proline or hydroxyproline

• Contains approximately 33% glycine, 30% proline/hydroxyproline, 37% other peptides.

Importance of Glycine Residues

• Stacks along inside of collagen molecule (shown in red)

• Glycine residues are important for maintaining tight turns (3 residues per turn).

• Provides flexibility of structure

Sequence Alignment

-Portion of collagen molecules from a human, mouse, chicken, and dog.-Shaded amino acids are conserved.

-Black=identical amino acids, Gray=similar amino acids, Blue=glycine, Pink=proline

Fibrils

Collagen molecules stack together to form fibrils. Above is an electron micrograph of several fibrils. One molecule of collagen from these fibrils are 3000Å in length and 15Å thick. The gaps formed between the collagen molecules line up every 4 molecules, causing striations that are 640Å.

Structure Stability

• Intramolecular Crosslinks: covalent bonds between residues inside a collagen molecule

• Intermolecular Crosslinks: covalent bonds of residues on different collagen molecules

Structure Stability

• Crosslinks usually occur between lysine, hydroxylysine, and histidine residues

Function

• Most abundant protein in humans and other vertebrates (comprises about 25-35% of total protein in the body)

• Provides flexibility/stability & comprises most of bones, connective tissues, tendons, ligaments, skin, etc

• Composes corneas• Roles in cell adhesion and signaling

– E.g. Human discoidin domain receptors DDR1 and DDR2 are activated by collagen

• Can be used for cosmetic and burn surgery• Denatures to form gelatin to use in food products,

pharmaceuticals, photography, and cosmetics.

Scurvy

• Occurs when vitamin C deficiency• Vitamin C is a cofactor for enzymes prolyl and lysyl

hydroxylase which hydroxylate proline and lysine.• Proline and lysine need to be hydroxylated for

crosslinking and hydrogen bonding (and therefore, stabilizing collagen).

• Leads to weakened connective tissues and capillaries.• Symptoms: bleeding of gums and bone/joint tissues,

bruising, hemorrhages, fatigue, yellowing skin.

Osteogenesis Imperfecta• Genetic disorder that causes fragile bones, low bone mass, and

problems with connective tissues (if person with disease survives at all)

• Usually caused by mutation of two genes for collagen I• The changes in coding cause a different amino acid to be substituted

for a glycine residue• Depending on the amino acid substituted, can be mild or lethal.

Osteogenesis Imperfecta

• Mild effect: Alanine substituted for a glycine

• Moderately severe effect: Cysteine, Serine, or Glutamic Acid substituted for a glycine

• Lethal effect: Arginine, Cysteine , Valine, Serine, or Aspartic Acid substituted for a glycine

*Pictures:Patient has cysteine in place of a glycine residue.

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