Term
| Which tissues are you least likely to find ECM proteins in? |
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Definition
| Epithelial cell layers and CNS |
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Term
| ECM proteins can be organized into "regular" and "irregular" structures. Provide examples of each. |
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Definition
Regular- tendon and ligament
Irregular- dermis and bone
Note- remember, the basement membrane is an ECM structure! |
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Term
Which class of ECM proteins has each function and what is their origin?
1) Cell adhesion, migration, differentiation and survival
2) Stress resistance
3) Shock absorption
4) Tissue protection and defense against infection
5) Elasticity of aorta, lung and cartilage |
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Definition
1) Glycoproteins (laminin and fibronectin)-
high MW, multidomain proteins originating (in the case of laminin) from epithelial and endothelial cells.
2) Collagens (collagen 1)
Linear molecules with triple-helical structure that originate from fibroblasts
3) Proteoglycans (aggrecan)
Core proteins with long carbohydrate side chains of dissacharide units that originate from chondrocytes.
4) Mucins
Core proteins with multiple, short carbohydrate side chains that originate from goblet cells
5) Elastic fibers
Arise from smooth muscle cells in blood vessels and chondrocytes in elastic cartilage. |
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Term
1) How does the triple-helicle structure of collagen arise?
2) What is the importance of glycine?
3) How is thermal stability achieved?
4) Why are they resistant to conventional proteases |
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Definition
1) GXY repeats (X is usually P and Y is usually hydroxy-P) form coiled-coil structures because of the abundance of proline. They exist as heterotrimers (type 1) and homotrimers (type 2) of alpha chains that are elongated, inflexible rods. These rods assemble to supra-molecular complex via non-collagenous N- and C-termini, which can be disrupted by pepsin.
2) Glycine allows tight packaging and H-bond formation b/w 3 chains- mutations disrupt helix formation
3) Post-translational hydroxylation of prolines raises the melting temperature above body temperature
4) peptide bonds are hidden within the helix, but can be accessed by collagenases from bacteria and fibroblasts (called matrix metalloproteases). |
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Term
| How are fibrillar collagens synthesized and processed? |
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Definition
1) During translation, peptides are transolcated to lumen of ER as pre-pro-peptide via signal sequence and SRP.
2) lysine (can also be glycosylated) and proline hydroxylation (Fe- and Vitamin C-dependent) occurs in ER.
3) Triple helix formation starts at C and "zips" towards the N-terminus, requiring C and N-terminal pro-peptides and chaperones.
4) Following secretion of pro-collagens, terminal pro-peptides are cleaved by endopeptidases, allowing side-to-side association and fibril formation (collagen 1 are aligned and cross-linked at terminal NC domains)
5) Cross-linking requires enzymatic oxidation of hydroxy-lysine and lysine by lysyl oxidase in an Fe and Vitamin C-dependent manner (not related to lysine-hydroxylase) |
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Term
When denatured, collagen 1 becomes gelatin.
1) What are the primary functions of collagen 1 when intact?
2) What disease is most commonly associated with collagen 1 and how does it manifest?
3) What other issues can arise? |
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Definition
1) Stress resistance (aortic rupture in knockout mice)
Bone formation
Cell adhesion
2) Osteogenesis imperfects (OI) arises from Glycine amino acid substitutions which lead to helix disruption and impairs bone formation and stability
3) Defective cleavage sites at N- or C- terminal pro-peptides or mutations in the C and N-terminal peptidases can also affect biosynthesis |
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Term
| What is Goodpasture syndrome? |
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Definition
Auto-antibodies attach collagen alpha3(IV).
Remember, collagen IV is the membrane-forming network of basement membrane collagen |
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Term
What is the primary action of each of the following glycoproteins and what is the result of it missing?
1) Fibronectin
2) Laminin-1
3) Laminin-2 |
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Definition
1) Homodimer that acts as a major cell adhesion protein (RGD sequence binds integrin at alpha5 beta1).
Defective vascular development.
2) Basement membrane composition and assembly. Cell adhesion, migration and neurite outgrowth.
Outer cell layer (basement membrane) dies off and pre-implantation death occurs (similar effect if beta 1 integrin or dystroglycan are missing/ laminin 1 receptors)
3) Adult myofiber basement membrane (contains alpha 2 subunit instead of alpha 1).
Mutations lead to congenital musular dystrophy, which becomes more severe with age. |
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Term
| How does arthritis (inflammation in joints) relate to proteoglycans? |
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Definition
| Proteoglycans have (-) charged side chains that attract Na+ and then water. Tissues rich in PGs are able to resist compression (cartilage). |
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Term
| What is Aggrecan and where is it made? |
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Definition
Modular Proteoglycan that has hyaluronic acid binding site at N-terminal domain and forms huge aggregates from a single acid linked to many PGs.
Synthesized in chondrocytes and 2nd largest contributor to cartilage, behind collagen 2. |
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Term
| A mutation in this type of molecule might result in erosion of the stomach lining due to lack of protection from HCl __________. |
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Definition
Mucins
The side chains of these molecules very often associate with sialic acid (i.e. they are (-) charged), and they are important for protecting the stomach from HCl |
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Term
1) Why are elastin polymers so resistant to alkaline hydrolysis?
2) How are they cross-linked?
3) What stains allow them to be visualized?
4) What disease is caused by mutations in the elastin gene? |
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Definition
1) They lack tryptophan, which makes them resistant.
Also, high A-content, highest V content (17%) and 30% G,, making thes proteins extremely hydrophobic.
2) Lysine cross-linking via lysyl-oxidase, requiring Cu, Fe and VitC.
3) Verhoeff (black) and orcein (purple)
4) Supravalvular Aortic Stenois (narrowing of aorta and pulm vein, leading to hypertrophy and hyperplasia of the intima and fibrosis)- can lead to MI and death. |
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Term
| What is the significance of the elastin-associated protein Fibrillin? |
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Definition
Marfan Syndrome!
important for myofibril formation. |
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