Collagen in the ECM Flashcards
What tissue contains collagen?
Where is collagen I found?
Where is collagen II found?
Where is collagen III found?
Where is collagen IV found?
bone, cartilage, skin, tendon and responsible for functional integrity and framework for structures
(Fibrillar form)Collagen I-bone, skin, tendon, cornea, other
(Fibrillar form)Collagen II-cartilage, vitreous of eye
(Fibrillar form)Collagen III-skin, blood vessels, others
(Network)Collagen IV-Basal lamina sheets
Distinguish fiber-forming and network-forming collagens and fibril associated collagens
Collagen self-assembles into small fibrils since it has been post-translationally processed. Fibers are an end-to-end aggregation of small fibrils forming longer fibrils that aggregate to form fibers.
Network forming collagens extend into multimers with no fibers and aggregate at the amino termini with a 7S domain. Networks are a scaffold for basal lamina.
Network collagens self assemble to form a chain link fence or sievelike structure
Fibril associated collagens- coat collagens to limit growth of the fiber or enhance the interaction of the fiber with the ECM. GAG chains of this type interact with collagens and other proteoglycan GAG chains
What are collagen specific amino acids?
What are the amino acid sequences of collagen?
Hydroxylation of glycines ,prolines, and lysines
Triple helical structure of special repeating sequence of amino acids GLY-X-Y with repeats of HYP and PRO
Gly occurs every 3rd AA
Describe the collagen helix feature
How is the collagen helix a basis for disease?
Triple helical proteins with 3 subunit polypeptides made of GLY-X-Y sequences
The crosslinking of the polypeptides provides the strength necessary for mechanical strength to withstand body stresses along with elasticity for heart beat in arteries.
Describe collagen assembly into fibers
How is the fiber stabilized by the crosslinks?
Collagen self assembly is followed by a stabilization by crosslinks
Crosslinks are essential for the fiber or network to withstand the physical stresses to which they are exposed
What is the pathway for normal degradation of collagen by collegenases called MMP?
How is it tightly controlled?
polymerized crosslinked collagen is cleaved by collagenase and subsequently the collagen molecules are degraded by other enzymes after the triple helical collagen is “unwound”
What are some of the disorders associated with defective formation of collagen?
Osteogenesis imperfecta; Scurvy; Ehlers-Danlos VI, VII, IX; Dermatosparaxis; Lathrism
What are 3 important features of collagen?
primary structural element in connective tissue, most abundant protein in mammals, highly post translationally processed
Describe the similarities of all collagens (3)
- All are made of 3 protein subunits wound around each other in a triple helix
- Triple helical structure requires a special repeating sequence of amino acids GLY-X-Y, and hydroxylation of prolines and lysines
- Cross-linking of polypeptides provides the strength necessary for mechanical strength to withstand body stresses along with elasticity
What type of collagen is found in vessels?
Type III
How is collagen assembled?
1/4 staggard with sticky ends out
Fibrils can assemble end to end to make a longer
Why is proline and hydroxyproline needed for fibers of collagen?
Proline is 2’ amine does not usually bend very well so a helix is formed due to the structural strain caused by proline
What is the most abundant protein and major structural protein?
collagen
T/F All collagens are triple helical proteins with 3 subunit polypeptides
True
What do collagen fibers self assemble from?
collagen subunits
In a collagen helix, where does the GLY-R group hydrogen face?
It faces into the core where there is only room for a H
What substance is needed the reaction to form hydroxyproline and hydroxylysine for the formation of collagen?
Vitaman C along with the appropriate hydroxylase enzyme (prolyl or lysyl)
Describe osteogenesis imperfecta
Collagen defect with a mutation of gly for cys but can be others
Cys is bulky and so the fibrils do not form well
Leads to the strength of collagenous tissues like bone being lowered that leads to multiple fractures
Which disease is a consequence for a loss of a glycine in collagen?
osteogenesis imperfecta
Which hydroxylated AA can be O-glycosylated for a collagen specific glycosylation?
Hydroxylysine
What is necessary for proper collagen formation and cross-linking?
hydroxyproline and hydroxylysine
If a patient is suspected of high rates of collagen turnover, what can be measured to to confirm this?
Urine which most of the turnover will come from bone resorption
Describe collagen biosynthesis from translation to secretion
- Synthesis of pro-alpha chain
- Hydroxylation of selected prolines and lysines
- glycosylation of selected hydroxylysines
- self-assembly of 3 pro-alpha chains
- procollagen triple-helix formation
- secretion
- cleavage of propeptides
Why are collagens synthesized as procollagen with non-collagenous globular portions?
help align the 3 strands to form a triple helix
Once the triple helix is formed, what happens to the globular domains?
must be removed before fibrillar collagens to become mature collagen ready to self-assemble into fibrils and fibers
After the assembly into fibers, how is collagen chemically cross-linked?
lysyl oxidase forms aldehydes of lysines and hydroxylysines
What defects occur when the collagen is not crosslinked correctly or procollagen processing?
defects result in abnormally elastic and weakened tissues
What does weak connective tissues result from?
improper biosynthesis, procollagen processing, and crosslinking
Where are collagen polypeptides translated? What 2 diseases are associated?
Translated into the RER where it is hydroxylated and glycosylated to properly form triple-helical collagen
Scurvy, Ehlers-Danlos VI lysyl hydroxylase
Ehlers-Danlos VII has a partial defect in what?
partial defect in N-pro-peptidase
T/F Cross-links necessary for collagen strength
True
Various collagen disorders help identify steps in formation of functional collagen.
What do the following diseases cause?
- GLY-X-Y repeats-
- PRO hydroxylation-
- LYS hydroxylation-
- Procollagen processing-
- Collagen fiber crosslinking-
- destabilized helix caused osteogenesis imperfecta
- collagen stability
- collagen stability
- collagen aggregation
- fiber strength
Why is the hydroxy-X important?
It can H bond to allow stabilization with in the helix
What are the 7 ways which collagen is degraded due to high regulation?
- requires activation of procollagenase
- matrix metalloproteinases (MMP) degrade collagen and other proteins
- Inhibitors called TIMPs regulate MMPs
- MMPs are involved in tissue development
- MMPs are involved in wound healing and inflammation
- MMPs are involved in cancer metastasis
- Bacteria make collagenases to destroy collagenous barriers to infection
What type of collagen is a network forming collagen?
Type IV and VIII
What does type IV collagen form?
Type IV collagen networks are a scaffold for what?
extended multimers and not fibers with aggregation at the amino termini which is a 7S domain
basal lamina
What type of collagen is a fibril associated collagen?
Type IX
Which type of collagen is associated on the surface of Type II collagen fibers and the globular ends have a GAG chain?
Type IX collagen monomer
T/F network forming collagens like type IV are components of basal lamina and other barriers to cells and macromolecules
True
What do fibril associated collagens like type IX coat collagens to do what?
limit growth of the fiber or enhance the interaction of the fiber with the ECM components
Collagen self-assembles into small fibrils after what?
post translationally processed
T/F Fiber forming collagens self assemble into long polymers.
T
T/F A typical collagen sequence is gly-x-y-x-y-gly-x-gly-y-, or 1/3 glycine.
F
T/F Vitamin C is required to form hydroxyproline from proline, and hydroxylysine from lysine.
T
T/F Hydroxylysine can be glycosylated.
T
T/F A meal which contains lots of proline can interfere with measurement of urinary hydroxyproline when assessing collagen turnover.
F
T/F Collagen is composed of 3 alpha-helical subunits
F
T/F The glycines are not as important in the gly-x-y repeat sequence compared to proline and hydroxyproline. This is evident from the lack of defects in collagen when glycines are replaced by other amino acids like cysteine.
F
T/F Scurvy, Ehlers-Danlos, and Mucopolysaccharidosis are collagen disorders.
F
T/F Elastin has desmosine, a crosslink requiring desmosine oxidase.
F
T/F Type IV collagen self aggregates to form fibrillar collagen.
F
T/F Collagen synthesis requires correct splicing of collagen mRNA.
T
Procollagen protease removes proline (Pro) from the C-terminal end.
F
T/F Translation - removal of procollagen globular ends (dumbells, blobs) - formation of triple helical structure.
F
T/F Alignment of three polypeptide chains in correct “register” - formation of triple helical structure - removal of procollagen globular ends.
T
T/F Secretion - aggregation to form structures (fibers) - crosslinking of collagen after lysyl oxidase activity.
T
