07b: CT and ECM Formation Flashcards
Primary structure of collagen molecule contains which key AA?
- Glycine
- Proline/hydroxyproline (imino acids)
- Lysine/hydroxylysine
Which AA is not found in collagen?
Cysteine
Collagen MW is (X). The triple helix has about (Y) number of AA residues.
X = 300 kDa Y = 3000 residues
Gelatin is essentially (X), which can occur in which environment?
X = denatured collagen
37oC (Tm)
Collagen, as a triple helix, has which special property that the three separate alpha chains don’t have?
Resistant to proteases
1/3 of collagen alpha chain is (X) AA.
X = glycine
1/4 of collagen alpha chain is (X) AA.
X = proline
The collagen triple helix is (RH/LH).
RH
The transcribed collagen alpha chains are (shorter/longer/same length as) final polypeptides. Explain.
Longer; presence of N-terminal leader sequence, N-terminal and C-terminal extensions
(Free/bound) ribosomes translated collagen alpha chains.
Bound; (translocated into ER)
First post-translational modification of collagen alpha chains:
Hydroxylation of proline and lysine residues in rER
Which enzyme hydroxylates (X) residues of collagen alpha helix?
- Prolyl hydroxylase (for proline residues)
2. Lysyl hydroxylase (for lysine residues)
Describe how scurvy occurs.
Deficiency of ascorbate (required via diet), which is cofactor for prolyl and lysyl hydroxylases; hydroxylation required for stabilization of collagen fibrils (cross-linking)
Symptoms of scurvy.
Skin lesions, fragile blood vessels, poor wound healing
Which post-translational modifications of collagen alpha helix take place in Golgi?
Glycosylation of select hydroxylysine residues
Genetic dysfunction of lysyl hydroxylase results in which disease?
Ehlers-Danlos syndrome
Clinical hallmarks of Ehlers-Danlos syndrome:
- Soft, hyper extensible skin
- Hypermobile joints
- Tissue fragility
Importance of hyroxylysines in collagen.
- Attachment sites for glycosyl residues
2. Critical in determining cross-linking pattern, stability, and tensile strength of collagen
Cure for Ehlers-Danlos.
Replace dysfunctional Lysyl hydroxylase enzyme (not impossible if done early)
T/F: Dysfunction of prolyl hydroxylase will also result in Ehlers-Danlos syndrome.
False
Lack of hydroxylated prolines in collagen has which effect?
Prevents secretion of pro-collagen from the cell
Collagen triple helix is stabilized at (X) end by (intra/inter)-molecular (Y) bonds.
X = C-terminal
Both intra- and inter-molecular
Y = disulfide
Once (X) is exocytosed from the cell, (Y) cleave the frayed ends, yielding (Z).
X = pro-collagen Y = pro-collagen peptidases Z = tropocollagen
Collagen fibril formation/alignment is driven by:
Ionic forces
A soluble collagen molecule is formed after:
Cleavage of pro-collagen N and C ends
What type of bonds are found in collagen fiber cross-links?
Covalent
Collagen fiber stabilization involves (X) enzyme, which specifically catalyzes which reaction?
X = lysyl oxidase
Oxidizes amino group in lysine/hydroxylysine into aldeghyde
Which side groups are crucial for forming the cross-links in collagen fiber?
Aldehyde groups (very reactive)
BAPN, aka (X), inhibits which enzyme/reaction in fiber synthesis?
X = beta-aminopropionitrile
Lysyl oxidase (cross-link formation in collagen fiber synthesis)
Cross-links formed in collagen fiber synthesis are (inter/intra)-molecular.
Both! Form between collagen chains and between separate collagen molecules
Mammalian collagenases cleave at which site(s)?
Make single split across the 3 alpha chains, 75% from N-terminal
What does cleavage by mammalian collagenases do to the fiber?
Decreases Tm to 30o (helices will denature at body T)
Half-life of collagen is:
tissue-specific
Waste products of collagen synthesis (such as N/C terminal extensions) end up in (X). Degradation products end up in (Y).
X = Y = urine/serum
Osteogenesis imperfecta is characterized by (X) symptom. What’s the cause?
X = brittle bones
Point mutations (replace glycine) in genes for alpha1 and alpha2 Type I collagen chains
In (X), why would mutations in alpha1 be (better/worse) than mutations in alpha2?
X = osteogenesis imperfecta
Worse;
Twice as many alpha1 per molecule
T/F: Osteogenesis imperfecta results in under-hydroxylation and glycosylation.
False - over-hydroxylation and glycosylation
Elastin is formed form (X) number of polypeptides.
X = 1
Which elastin residue(s) is/are glycosylated?
None!
Which AA is quite abundant in elastin, giving it (X) characteristic.
X = hydrophobic (90% of elastin is hydrophobic)
Valine
33% of elastin molecule is (X) AA. 20% of elastin molecule is (Y)% AA.
X = glycine Y = proline
Which elastin residue(s) is/are hydroxylated?
None!
MW of elastin.
69 kDa
Names of cross-links in elastin.
Desmosine and Isodesmosine
Emphysema is a result of:
Destruction of elastic fibers of lung
Turnover of elastin is (fast/slow)
Very slow
When is elastin soluble?
Soluble elastin molecule (tropoelastin) synthesized in cell, but upon secretion to extracellular fluid, cross-links form and make it highly insoluble
Cross-linking of elastin carried out by which enzyme?
Lysyl oxidase
Factors that cause imbalance and, thus, emphysema.
- Anti protease inhibitor deficiency
2. Smoking
Absence of MFAP-4 has which effect on (X) process?
X = elastic fiber formation
Without MFAP-4, fibrillin-1 can’t form microfibrils, which cross-link with tropo-elastins to allow proper formation of elastic fibers
GAGs are (mono/di/poly)-saccharides with which (non-repeating/repeating) unit(s)?
Polysaccharides; repeating disaccharide units:
- Uronic acid
- Amino sugar
Proteoglycans are primarily synthesized in (X) and degraded in (Y).
X = ER Y = lysosomes
