Connective Tissue - Franzblau Flashcards
when does a polypeptide become a protein?
when it has biological activity
“proteus” is the greek root for…
“of highest importance”
growth of connective tissue in the lumen of a blood vessel is called
atherosclerosis
emphysema is caused by
destruction of elastin fibers in lungs
atherosclerosis is caused by
growth of connective tissue in the lumen of a blood vessel is called
cirrhosis is caused by
fibrosis of liver
ehlers-danlos syndrom is caused by
genetic mutation in collagen metabolism
how many distinct collagen polypeptides are there
> 18
how many polypeptides in a mature collagen protein
3 wound together
what is the length and width of a mature collagen protein
300nm by 1.5 nm
molecular weight of mature collagen protein
285 kDa
idiopathic means
of an unknown cause
collagen accounts for roughly how much vertebrate protein weight?
1/4th
one third of all collagen amino acid residues are…
glycine
three common and essential aa residues of collagen are….
glycine
proline & hydroxyproline
lysine & hydroxylysine
hydroxylysine is hydroxylated on the __ carbon
δ
T/F there are no cystein residues in most mature collagen proteins
true
what is the general alternating regional sequence of collagen amino acid residues?
regions of gly pro x (nonpolar usually)
regions of gly x x (polar usually)
(x can be hydroxypro, hydroxylys, or others)
is proline typically polar or nonpolar?
nonpolar
what is the rise per residue of an alpha helix vs collagen alpha chain helix?
.15 nm vs .28 nm
1.5 A vs 2.8 A
what is a type II trans helix
a left-handed polyproline helix (.28 nm rise)
found in collagen α chains
is the collagen helix left or right-handed?
left
how many α chains form a collagen helix?
3
are α chains in a collagen helix wound around each other in a left or right-handed fashions
right
why is glycine important in triple helix formation?
gly is the only aa that can fit in these tightly bound triple helixes
mutations exchanging glycine residues for other aa residues in collagen may result in what kind of pathology?
brittle bones e.g. osteogenesis imperfecta
tropocollagen
complete functional 3-stranded collagen molecule
how do tropocollagen molecules line up to form a fibril?
head to tail and staggered by 25%
how much are adjacent tropocollagen fibrils staggered by?
25%
what is the molecular weight of an amino acid on average?
100 daltons
how many amino acids in a 100,000 Da polypeptide?
1,000
100 daltons / amino acid
how many amino acids in 100 kDa polypeptide
1,000
100 daltons / amino acid
.1 kDa / amino acid
are all 3 α chains in a tropocollagen molecule identical?
usually not
e.g. collagen I is α1 2α2
what is the α chain structure of collagen I?
α1 2α2
T/F the α1 chain of different collagen types are genetically distinct
true
α1 just denotes the first type of α-chain in that collagen, it is not universal nomenclature
where is collagen I found
skin tendon bone cornea (70% of all collagen)
which is the most common collagen type?
collagen I (70% of all collagen)
collagen II is found…
in cartilage
collagen III is found…
in reticular fibers
collagen IV is found…
in basement membranes
outline the entire collagen synthesis pathway from transcription to turnover
transcription translation hydroxylation in ER glycosylation in Golgi pro-collagen triple helix extrusion from cell tropocollagen (termini cleaved) fiber formation fiber stabilization turnover/repair
where are collagen α-chains hydroxylated?
ER
where are collagen α-chains glycosylated?
Golgi
where is procollagen cleaved into tropocollagen?
ECM
what is collagen biosynthetic intermediate that is extruded from the cell?
procollagen (triple helix with terminal tangles)
what process in collagen biosynthesis gives rise to microheterogeneity of α-chains?
hydroxylation in ER
glycosylation in Golgi
what is the enzymes that modify collagen in the ER?
prolyl hydroxylase
lysyl hydroxylase
T/F prolyl hydroxylase and lysyl hydroxylase modifie free proline and lysine
false - only hydroxylate proline and lysine in pp chains
which is more commonly hydroxylated on proline, C3 or C4?
C4, but C3 possible
what is the cofactor for prolyl hydroxylase?
ascorbate (from diet)
lack causes scurvy
ascorbate is a cofactor of which collagen biosynthetic enzyme?
prolyl hydroxylase
the cofactor in the collagen biosynthetic pathway that causes scurvy if lacked is called __ and it interacts with enzyme __
ascorbate
prolyl hydroxylase
why does ascorbate lack result in scurvy?
ascorbate is a cofactor for prolyl hydroxylase
lack = fewer hydroxylations, failure to stabilize collagen fibrils through x-linking
which number C does lysyl hydroxylase hydroxylate?
C5 (δ)
ehlers-danlos syndrome is caused by a mutation in which collagen biosynthetic enzyme?
lysyl hydroxylase
prolyl hydroxylase problems are fatal in utero
what is a cofactor for lysyl hydroxylase?
ascorbate
is ascorbate a cofactor for prolyl hydroxylase or lysyl hydroxylase?
both
what interactions stabilize procollagen through the terminal extensions?
disulfide bonds
where in collagen are disulfide bonds found?
on the terminal ends of procollagen
but these are cleaved off in functional tropocollagen and mature collagen fibers
which terminal extensions bind together first in procollagen formation?
C-terminals (through disulfide bonds)
then procollagen wraps up to N-terminus
with reference to collagen, Tm is the temperature at which…
50% of the helical structure is lost
the temperature at which 50% of collagen helical structure is lost is called
Tm (melting temperature)
what is the Tm of:
gly-pro-pro collagen sequences
gly-pro-hyp collagen sequences
collagen as a whole
gly-pro-pro = 24 degrees C gly-pro-hyp = 58 degrees C overall = 37 degrees C
what is the melting temperature of collagen
37 degrees C
roughly physiologic, we teeter on the edge of stability… but there are other stabilizing forces present
T/F the collagen triple helix is remarkable stable under physiological conditions
true - but it will denature when heated
what does the typical melting curve (heat denaturation curve) of collagen look like
~100% helix content until sudden drop-off near 37 degrees C (Tm)
50% helix content at 37 degrees C
what enzyme cleaves procollagen into tropocollagen?
procollagen peptidases
what is the function of procollagen peptidases in collagen biosynthesis?
cleave terminal extensions from procollagen and it becomes tropocollagen
what collagen type is not cleaved from procollagen to tropocollagen by procallagen peptidase?
type IV collagen (basement membranes)
gaps between head-tail tropocollagens in fibers are __ nm
42 nm
adjacent tropocollagen rows are displaced __ nm in fibers
68 nm
roughly 1/4th of 300nm total
what forces drive the quarter stagger of tropocollagen in collagen fibrils?
polar and non-polar forces
how are collagen fibers formed vs stabilized?
formed: polar and non-polar interactions line tropocollagen up head-tail and quarter stagger
stabilized: covalent cross-linking through lysil oxidase and aldol condensations and also 3 lysyl hydroxypyridinium rings
2 types of x-linkage to stabilize collagen
- aldol cross links: lysyl oxidase LOX turns lysyl amino groups into aldehyde groups, which bind to each other through aldol condensations
- hydroxypyridinium ring (pyridinoline) formation betwen two hydroxylysyl and one lysyl residue
how does osteogenesis imperfecta come about and what are the symptoms
- mutations impair collagen triple helix formation (gly substituded with sterically bulkier residues), leads to over hydroxylation & glycosylation because helices are not wound as tightly
- brittle bones, frequent fractures
what happens in the disease lathyrism caused by ingestion of β-aminopropionitirile BAPN which is found in sweet peas?
BAPN is suicide inhibitor of LOX, so aldol cross-linking of collagen fibers reduced
T/F collagen is a static protein
false - synthesis and degredation are dynamic and balanced, not static
what enzymes participate in collagen turnover and repair?
collagenases
how do collagenases work in collagen turnover and repair?
-cleave collagen, decreasing Tm from ~37 to ~30 degrees C
escribe 3 steps of collagen turnover and repair
- collagenases cleave collagen, decreasing Tm from ~37 to ~30 degrees C
- denatured collagen α-chains are degraded non-specifically by other proteases
- degredation products may feedback to new collagen production
what is the approximate rate of collagen turnover?
~50% turnover every 3-4 weeks
how does the quaternary structure of elastin differ from collagen?
elastin = no quaternary structure (single pp only) colagen = 3 α-chains
elastin contains __-rich non-polar regions that participate in hydrophobic interactions
valine
elastin fibers associate with one another through what kind of interactions?
covalently cross-links
what is the principle stabilizes elastin fibers?
entropy - stretched = less entropy, wants to recoil
the monomeric precurser to to elastin fibers is called
tropoelastin
tropoelastin is
the monomeric precurser to to elastin fibers
in what form is elastin when it moves from intracellular to ECM?
tropoelastin
where is tropoelastin found?
ICM, secreted to ECM to cross-link and form elastin fibers
what enzyme facilitates elastin cross-links?
LOX lysyl oxidase
does LOX lysyl oxidase facilitate cross-linking of elastin or collagen?
both
what is an alysyne residue
a lysine with amino turned aldehyde
how does elastin corss-linking occur?
- lysyl oxidase LOX oxidises 3 lysine residues into aldehyde (alysine) residues
- these 3 alysine react with a fourth lysine to form desmosine, a 4 lysyl ring structure
what is a desmosine
a 4 lysyl ring structure that cross-links elastin fibers
marfan syndrome is cause by
missing fibrillin gene (fibrillin is a component of collagen)
what is the half-life of elastin?
70-80 years
what is the half-life of collagen?
3-4 weeks
how does the half-life of elastin compare to that of collagen?
much longer
70-80 years vs 3-4 weeks
what are 2 possible causes of emphysema?
smoking
α-1 antitrypsin deficiency
what amino acid residues to GAGs bind to?
serine residues (O-linked)
GAGs are polysaccharides formed by repeating __ __ units
repeating amino-disaccharide units
chondroiotin sulfate heparan sulfate keratan sulfate hyalurononan are all examples of
GAGs
what is a proteoglycan
protein + GAGs
aggrecan and decorin are examples of
proteoglycans
which has more GAG chains, aggrecan or decorin
aggrecan - 100 GAGs
decorin - 1 GAG (with N-linked oligosaccharides)
what is the charge of GAGs
negative (sulfate and carboxyl groups)
what gives GAGs their negative charge?
sulfate and carboxyl groups
this protein binds cells and collagen fibers together
fibronectin
name 4 components of a typical proteoglycan
hyaluronic acid backbone
linker protein (hylauronic acid to core proteins)
core proteins (branching off hyaluronic acid)
GAGs (branching off core proteins)
T/F H-bonds between aa’s in neighboring collagen chains stabilize the structure
true
T/F proteoglycans function in all of the following:
- structure
- aid cell adhesion
- determine viscoelastic properties
- withstand compression
- facilitate contact between ligands and receptors
- serve as reservoir of growth factors
- protect proteins from proteolytic degredation
true
T/F proteoglycand facilitate protein degredation
false - they protect proteins from proteolytic cleavage
what is the difference between:
hydroxypyridinium (pyridinoline)
desmosine
hydroxypyridinium (pyridinoline) - collagen cross links (3 lysyl residues)
desmosine - elastin cross links (4 lysyl residues)
