Protein Structure - Collagen

Collagen 1 Protein Structure – Collagen Most abundant protein in mammals Extracellular: cartilage, tendons, bones, teeth, skin, vessels, lungs 3000 Å 97 Protein Structure – Collagen Primary & Secondary structure Primary structure Amino Acid composition Secondary structure Ramachandran plot f = -65° y = +130° CD of collagen Amino Acid Sequence (Gly-Pro/Ala-X)330 random coil X=hydroxyl-Pro, Glx, Arg, Asx, hydroxyl-Lys (Cd), Ser Hydroxylation reactions catalyzed by proline- and lysine-hydroxylase; require vitamin C 2 Protein Structure – Collagen Protein Structure – Collagen The 4 S’s for Collagen: Size Shape Stability Solubility 3 Protein Structure – Collagen F (°) y (°) (Dist/residue) (Å) a-helix -57 -47 Anti- ⇌ b-sheet -139 Parallel ⥤ b-sheet -119 Structure Rise (Distance/repeat) 1.5 3.6 5.4 5.0 +135 3.4 2 6.8 - +113 3.2 2 6.4 - 4 0 - 4 0 - 3 9 b-turn-Type I i+1 -60 -30 - i+2 -90 0 - b-turn-Type II i+1 -60 120 - i+2 80 0 - -65* +130* 3 Collagen Pitch Diameter (Å) Residues/ Repeat (Å) 14-16 (triple) Size MW = 285,000 Da Long strands (3000 x 14-16 Å) helix dimensions/parameters Protein Structure – Collagen The Collagen Triple Helix C N 16 Å Shape; Collagen-triple helix left handed right handed twist to three helices role of glycine Allows for packing of triple helix role of proline Locks the helix 4 Protein Structure – Collagen Stability Packing of Gly Inter-stand H-bonds OH-P P G Inter-chain H-bonds Protein Structure – Collagen Stability Melting (viscosity or CD vs. temp) cooperativity = sigmoidal plot role of hydroxyl-proline- Tm Melting of Collagen Species Body Temperature Calf 37 Shark, barracuda 26 Cod, deep sea redfish 14 Collagen Tm 39 29 16 50% Higher Tm correlates with higher OH-Pro/Pro Tm=39° 5 Protein Structure – Collagen Pro Pro-OH Gly (Gly-Pro/Ala-X)330 (Gly-Pro-Prohydroxy) X=hydroxyl-Pro, Glx, Arg, Asx, hydroxyl-Lys (Cd), Ser Protein Structure – Collagen The 4 S’s for Collagen: ✓ ✓ ✓ Size Shape Stability Solubility - not 6 Protein Structure – Collagen Modified Residues in Collagen & Elastin 1.4-9% 0.5-3% Protein Structure – Collagen Prolylhydroxylase ox red Lysylhydroxylase (uses a similar mechanism) Scurvy: Vitamin C Deficiency 7 Protein Structure – Collagen Cross-linking of Collagen Solubility: insoluble due to cross-linking between FOUR triple helices using 3 Lys and 1 His residues lysyl oxidase à allysine LTQ cofactor merodesmosine Protein Structure – Collagen Cross-linking of Collagen NH3 NH3 Allysine aldol 8 Protein Structure – Collagen The 4 S’s for Collagen: ✓ ✓ ✓ ✓ Size: Long strands (3000 x 14 Å; ~300 Kda) Shape: left-handed triple helix Stability: controlled by degree of Pro-OH Solubility: - not How and where is collagen produced? biosynthesis Protein Structure – Collagen 1) 2) 3) 4) 5) 6) 7) Transcription & translation Protein modification – hydroxylation – glycosylation quaternary structure & disulfides Secretion Procollagen processing Cross-linking Deposition Collagen Biosynthesis 117 9 Protein Structure – Collagen Collagen Disorders One thousand mutations have been identified in twelve out of more than twenty types of collagen. These mutations can lead to various diseases at the tissue level Diseases Scurvy – caused by lack of Vitamin C needed for hydroxylating enzyme that makes Pro-OH (Hyp) & Lys-OH (Hyl) Osteogenesis imperfecta – caused by a mutation in type 1 collagen weak bones and irregular connective tissue Ehlers-Danlos Syndrome – caused by a mutation in type 3 collagen (EDS, type 4) Ten different types of this disorder that lead to deformities in connective tissue. Osteoporosis – Not inherited genetically, brought on with age reduced levels of collagen in the skin and bone Knobloch syndrome – Caused by a mutation in the collagen XVIII gene protrusion of the brain tissue and degeneration of the retina 10