REINHART 5

Question 1

how many chains make up collagen

Answer 1

3 alpha chains (NOT alpha helix)
triple helix
homotrimers or heterotrimers
forms aggregates by association of triple helices

Question 2

how many collagen genes are there?

Answer 2

46 genes

Question 3

how many collagen types are there?

Answer 3

28 collagen types

Question 4

what structures do collagens form?

Answer 4

fibril and sheets

Question 5

what are the orientation of the alpha chains of collagen? (single and trimer)

Answer 5

single chain: left handed, counter clockwise
trimer: right handed, clockwise

Question 6

what amino acids are collagen chains made of?

Answer 6

(Gly-X-Y) repeat
X- often proline
Y- often hydroxyproline

Question 7

what are the orientations of the amino acids in the chain?

Answer 7

glycine is oriented towards the inside
smallest amino acid
proline’s ring structure acts as a stabiliser of the helix

Question 8

what are the collagen precursors called?

Answer 8

pro alpha chains

Question 9

what modifications happen to those alpha chains? (in the ER)

Answer 9

hydroxylation
gycoylation: monossaccharide glucose or Disacharide Glycosylgalactose

Question 10

what is the role of the propeptide?

Answer 10

guide intracellular formation of the triple-stranded collagen molecules
prevent intracellular formation of large collagen fibrils

Question 11

how does collagen assembly happen?

Answer 11

happens after secretion
cleavage of propeptides
self assembly into fibrils
aggregation of collagen fibrils to make a collagen fibers (because less soluble)

Question 12

what happens in extracellular procollagen processing?

Answer 12

• Procollagen N-proteinase
• Procollagen C-proteinase
• both members of zinc binding metalloproteases
• removal of the Collgen propeptide

Question 13

what is the structure of a generic collagen microfibril?

Answer 13

• Triple helix ~ 300 nm in length, ~ 1000 amino acid residues

Question 14

how can collagen molecules assemble after secretion into the ECM?

Answer 14

into higher order polymers
many hundreds micrometers long
clearly visible by EM, sometimes even light microscopy

Question 15

what happens to the collagen amino acids after secretion in ER lumen?

Answer 15

selected prolines and lysines are hydoxylated
Hydroxyproline at gamma position (stabilization by interchain hydrogen bonds)
hydroxylysine at delta position (some become glycosylated, mono- or disaccharide)
Both modified amino acid residues are infrequently found in other animal proteins

Question 16

what are the purposes of lysyl hydroxylation?

Answer 16

Lysyl hydroxylation serves 2 reasons:
attachment sites for a monosacharide or disacharide (galactose, or glycosylgalactose)
crosslink sites

Question 17

what is 4-hydroxyproline essential for?

Answer 17

4-hydroxyproline is essential for collagen stability (intermolecular) hydrogen bonding
P4H knockout in mice: lethal

Question 18

which enzyme hydroxylases proline?

Answer 18

Prolyl hydroxylase (Prolyl 4-hydroxylase)
3 known isoenzymes

Question 19

what enzyme hydroxylates lysines?

Answer 19

Lysyl hydroxylase:
3 known isoenzymes (LH-1, LH-2, LH-3)

Question 20

what does lysine hydroxylation determine?

Answer 20

lysine hydroxylation defines types of crosslinks
LH-1 defect: Ehler-Danlos syndrome type VI
LH-2 defect: Bruck syndrome
LH-3 knockout in mouse: lethal

Question 21

what does the mechanism of prolyl hydroxylase require?

Answer 21

dioxygenase
requires Fe2+ (ferrous ion) in active center

Question 22

what does vitamin C do?

Answer 22

Vitamin C (regenerates Fe3+ to Fe2+)

Question 23

what happens in the absence of a substrate?

Answer 23

In the absence of the substrate: iron (Fe2+) is oxidized to ferric ion (Fe3+) this then inactivates the enzyme

Question 24

what are consequences of defective collagen production?

Answer 24

rupturing of blood vessels
defective wound healing
bleeding gums -> loss of teeth
if not treated results in death

Question 25

what are lysyl oxidases (LOX) dependent on?

Answer 25

LOX and 4 Lox-like proteins (copper-dependent)
make covalent cross links

Question 26

what strengthens LOX?

Answer 26

greatly strengthened by formation of covalent cross-links between lysine residues

Question 27

what can collagen defects cause?

Answer 27

ehlers-danlos syndrome
- flexible loose joint
- loose stretchy skin
- excessive fragility of the skin, blood vessels and other tissue

Question 28

what are disintegrins?

Answer 28

proteins containing a large number of cysteine residues (lots of disulfide bonds)
small proteins (40-100aa)
block function of some integrins
act as competitive inhibitors for integrin-fibrin interaction and block blood coagulation