Extracellular Matrix- Molecules and Cells in Health and Disease

What is the repeating units in all collagens?

glycine-proline-Y

glycine-X-hydroxyproline

What function does proline in the repeating unit of collagen give?

Tight wrapping of the three chains arround one another

Two amino acid products that form intrachain hydrogen bonds between collagen molecules

hydroxyproline

hyrdoxylysine

What bond can hydroxylysine form in collagen and how?

Covalent bonds with other lysines/hydroxylysines. Deanimated by Lysil Oxidase (LOX)

Role of Vitamin C in scurvy

Vitamin C is a cofactor for proline hydroxylase and lysyl hydroxylase

Without vitamin C, hydroxyproline and hydroxylysine are not formed

No covalent or hydrogen bonds between collagen fibres

ECM not as strong

What collagen makes up basement membranes?

Collagen IV

Two examples of diseases caused by loss of basement membrane strength

Epidermyolysis Bullosa and Muscular dystrophy

Difference between Collagen IV and Collagen I

Non collagenous regions are not cleaved

Coiled coil region has interruptions within the Gly-X-Y repeats- increasing flexibility and number of sites for cross linking.

What amino acids are rich in the N-term of collagen IV

Cys and Lys

Name for C-term of collagen

NC1

Name for N-Term on collagen

7S domain

What part of collagen IV monomers interacts to form a trimer

NC1- each domain has a docking site and beta hairpin for domain swapping

Where do collagen monomers form trimers?

The ER

What happens once a IV collagen trimer is secreted from the ER

NC1 trimers interact with another NC1 trimer to form a hexamer

7S domains interact with one another to form a tetramer of collagen trimers

What causes collagen to become ordered into basement membranes?

Self assembles

How many types of collagen IV genes are there?

6

What are the three possible combinations of different collagen chains

a1a1a2

a3a4a5

a5a5a6

What chains is most collagen in the body made up of?

a1a1a2

Body part with a specialised BM and the BMs function

Glomerular

Thicker BM that are important for filteration

What two cell layers does the glomerular BM seperate?

Endothelial cells of the blood vessels and podocytes

what part of the kidney expresses a1a1a2 isoform

Bowmans capsule

How does collagen type change in the kidney from development to maturation

In development a1a1a2 is expressed in the the GBM which switches to a3a4a5 as the kidney matures

Whats wrong with the GBM in alports syndrome?

Mutation in a3a4a5 isoform- either reduced functioning or loss of function so a1a1a2 takes over

a3a4a5 has more crosslinks that protects it from increased pressure and proteolysis from proteases in serum

GBM made up of a1a1a2 breakds own- leads to disease

Most common gene to mutate in X-linked Alports?

COL4A5

What does Alports syndrome lead to

End stage renal disease

In about 20 years in early onset, and by 40 years in slow progressing, adult type

Mutation in what genes are associated with autosomal recessive forms of Alports

Col4A3 and Col4A4

Why is alports more common in men?

COL4A5 and COL4A6 are both on the X chromosome

Where are Collagen IV Alport mutations most likely to take place?

The coiled coil region

What kind of mutations in collagen IV would you expect to see in early onset alports?

Large gene rearrangements

Non-sense mutations and splice sites leading to truncation

What kind of mutations in collagen IV would you expect to see in late onset alports?

missense mutations disrupting repeats

Conserved cystein residues affecting crosslinking

What is a potential treatment for Alports

ACE inhibitors

Reduce pressure in glomerulus- increases life span in Alports Mice

Role of the basement membrane

Structural support

Modify cell behaviour

Four major components of BM

IV collagen, laminin. nidogen/entactin and perlecan

How many chains are there in the laminin protein family?

11

Names of the laminin chains

alpha 1-5, beta 1-3, and gamma 1-3

What is at the C terminal of alpha laminin chains?

The G domain made up of five homologous LG domains

How many laminins are there?

15

Structure of Nidogen

Three G domains with G1 at the N terminal and G3 at the C terminal

A short rod separates domains 1 and 2 and a long rod seperate domains 2 and 3

How many types of nidiogen are there?

2

Which type of nidogen is predominant in vascular BM

nidogen2

What is Nidogen essential for

function of BM of organs, specifically lungs and heart.

Nidogen is…

a) a protein

b) a lipid

c) a glycoprotein

d) a phospholipid

c a glycoprotein

Structure of perlecan

5 distinct domains (pearls on a string)

structure of laminin

Three chains- one alpha, one beta and one gamma

These chains form an alpha helix at the C-Terminal, then separate into three prongs

Formation of Laminin

In the Golgi, beta-gamma dimers form

This is stabilized and secreted by incorporation of the alpha chain

Where do laminins bind to each other

alpha-VI domain, beta VI domain, gamma VI domain