Biochemistry of Collagen

Question 1

What are some of the roles of the ECM?

Answer 1

• Provides a scaffold for tissue development.
• Provides a mechanical basis for cell attatchment and movement
• Transmits force
• Can withstand compression in cartilage and IVD
• ECM provides survival signals to cells and differentiation signals to stem cells.
• Is a resevoir for growth factors

Question 2

What molecules comprise ECM?

Answer 2

• Water (50%)
• Proteins
• Glycoproteins
• Proteoglycans
• Glycosaminoglycans

Question 3

What are glycoproteins?

Answer 3

-Proteins with a carbohydrate side chain:
sugars (glucose, galactose)
amino sugars (N-acetylglucosamine)
Acidic sugars (salic acid)
-Attatched by glycosylation in golgi by glycosyltransferase

Question 4

What are proteoglycans and what do they allow?

Answer 4

• Heavily glycosylated protein with GAG side chain (eg. chondroitin sulfate)
• Acid group provides negative charge to allow water attraction and protection against compressive forces.

Question 5

How many collagen types are there and how does this affect structure?

Answer 5

• Around 30

- All do different things so are organised in different structures

Question 6

Give some examples of collagen types and their role?

Answer 6

• Fibril forming: tensile strength
• Bead forming: elasticity, long range connectivity
• Transmembrane: cell-matrix interactions (perhaps signalling)

Question 7

What are collagen fibrils important for?

Answer 7

• The most common building block of tissues

- Collagen makes up 30% of protein mass and is a major component of connective tissue.

Question 8

What is the structure of collagen?

Answer 8

• Triple helix structure
• Gly-X-Y repeat
• X and Y can be any amino acid but often are proline and hydroxyproline)
• Glycine always located at centre of triple helix

Question 9

What does collagen give?

Answer 9

-Tensile strength

Question 10

Describe the process of collagen maturation?

Answer 10

• Synthesis of pro alpha chain
• Hydoxylation of selected prolines and lysines, carried out by hydroxylase enzyme using Vit C and molecular O2 to do so.
• Glycosylation of selected hydroxylysines.
• Self assembly of 3 pro alpha chain
• procollagen triple helix formation
• Secretion
• Cleavage of propeptides
• Self assembly into fibril
• Aggregation of collagen fibrils to form a collagen fibre.

Question 11

What enzymes are used to hydroxylate lysyl and prolines?

Answer 11

-Different hydroxylase enzymes for lysyl and prolines.

Question 12

What mutations can lead to collagen diseases and what do they often affect?

Answer 12

• Most often, mutations affect glycine

- Often affects multiple organs/tissues

Question 13

What is OI and what happens in it?

Answer 13

• Brittle bone disease

- Collagen type 1 related disorder

Question 14

What are clinical severities of OI?

Answer 14

Range from fractures to lethality.

Question 15

What is the common type of OI and what is mutated in it?

Answer 15

• Autosomal dominant
• COL1A1 or COL1A2 are mostly mutated
• Accounts for over 90% of OI cases.

Question 16

What is a less severe type of OI and describe what happens?

Answer 16

• Type 1
• Less severe, no symptoms at birth
• Due to null mutations (prevent/stop collagen being formed).
• Reduced collagen
• Collagen made still good quality
• Can lead to early onset of osteoporosis

Question 17

What mutations may lead to type 1 OI?

Answer 17

• Stop codons (not enough collagen made as stopped early)
• Promoter mutations
• mRNA instability

Question 18

What mutations occur in more severe OI forms?

Answer 18

-80% glycine missense mutations

Question 19

What does more severe forms of OI lead to?

Answer 19

• Effect on modification due to delay in folding
• Quality of collagen severly impacted
• Disruption of the gly-x-y sequence slows the rate of folding resulting in over modification of the chains N-terminal.