REINHART 5 Flashcards
how many chains make up collagen
3 alpha chains (NOT alpha helix)
triple helix
homotrimers or heterotrimers
forms aggregates by association of triple helices
how many collagen genes are there?
46 genes
how many collagen types are there?
28 collagen types
what structures do collagens form?
fibril and sheets
what are the orientation of the alpha chains of collagen? (single and trimer)
single chain: left handed, counter clockwise
trimer: right handed, clockwise
what amino acids are collagen chains made of?
(Gly-X-Y) repeat
X- often proline
Y- often hydroxyproline
what are the orientations of the amino acids in the chain?
glycine is oriented towards the inside
smallest amino acid
proline’s ring structure acts as a stabiliser of the helix
what are the collagen precursors called?
pro alpha chains
what modifications happen to those alpha chains? (in the ER)
hydroxylation
gycoylation: monossaccharide glucose or Disacharide Glycosylgalactose
what is the role of the propeptide?
guide intracellular formation of the triple-stranded collagen molecules
prevent intracellular formation of large collagen fibrils
how does collagen assembly happen?
happens after secretion
cleavage of propeptides
self assembly into fibrils
aggregation of collagen fibrils to make a collagen fibers (because less soluble)
what happens in extracellular procollagen processing?
- Procollagen N-proteinase
- Procollagen C-proteinase
- both members of zinc binding metalloproteases
- removal of the Collgen propeptide
what is the structure of a generic collagen microfibril?
- Triple helix ~ 300 nm in length, ~ 1000 amino acid residues
how can collagen molecules assemble after secretion into the ECM?
into higher order polymers
many hundreds micrometers long
clearly visible by EM, sometimes even light microscopy
what happens to the collagen amino acids after secretion in ER lumen?
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
what are the purposes of lysyl hydroxylation?
Lysyl hydroxylation serves 2 reasons:
attachment sites for a monosacharide or disacharide (galactose, or glycosylgalactose)
crosslink sites
what is 4-hydroxyproline essential for?
4-hydroxyproline is essential for collagen stability (intermolecular) hydrogen bonding
P4H knockout in mice: lethal
which enzyme hydroxylases proline?
Prolyl hydroxylase (Prolyl 4-hydroxylase)
3 known isoenzymes
what enzyme hydroxylates lysines?
Lysyl hydroxylase:
3 known isoenzymes (LH-1, LH-2, LH-3)
what does lysine hydroxylation determine?
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
what does the mechanism of prolyl hydroxylase require?
dioxygenase
requires Fe2+ (ferrous ion) in active center
what does vitamin C do?
Vitamin C (regenerates Fe3+ to Fe2+)
what happens in the absence of a substrate?
In the absence of the substrate: iron (Fe2+) is oxidized to ferric ion (Fe3+) this then inactivates the enzyme
what are consequences of defective collagen production?
rupturing of blood vessels
defective wound healing
bleeding gums -> loss of teeth
if not treated results in death
what are lysyl oxidases (LOX) dependent on?
LOX and 4 Lox-like proteins (copper-dependent)
make covalent cross links
what strengthens LOX?
greatly strengthened by formation of covalent cross-links between lysine residues
what can collagen defects cause?
ehlers-danlos syndrome
- flexible loose joint
- loose stretchy skin
- excessive fragility of the skin, blood vessels and other tissue
what are disintegrins?
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
