6 Extracellular Matrix Biology II Flashcards
*Q: What is the size of most ECM proteins? What’s their architecture? Function? Adhesion?
A: Most ECM proteins are very LARGE
They have MODULAR architecture - they are composed of protein domains of 50-200 amino acid residues (each of the units in the diagram is a protein molecule)
multifunctionality of ECM proteins is a result of their modular structure (different domains give different functions)
many large modular proteins are multi-adhesive, binding various matrix components and cell surface receptors
*Q: Draw a diagram for perlecan. What is it?
A: basement membrane proteoglycan
sugar chains
\ /
o»[]o0o0[][][][][][]<><><><>
immunoglobulin-like (IG) domain
*Q: What are laminins? Size? Where are they found? What do they interact with? Adhesion?
A: - ubiquitous basement membrane glycoproteins (in ALL basement membranes)
- very large
- Interact with cell surface receptors // Can self-associate as part of the basement membrane matrix and can interact with other ECM components
- Multi-adhesive
*Q: What are laminins derived from? Mutations?
A: Derived from several genes
Mutations associated with inherited disease e.g. muscular dystrophy and epidermolysis bullosa.
*Q: Draw a diagram for a laminin molecule and label.
A: Contains of 3 chains = Forms a CROSS-SHAPED MOLECULE (on its side)
Different regions on the laminin have different binding capacities . NH2 . | . 2 . | H2N-----1-----------------------------4----------------------------5 . | . 3 . | . NH2
- alpha chain (at end, allows binding to integrin)
- beta chain (at end allows self-assembly)
- gamma chain (at end allows self-assembly)
- > just above 3 = binding zone for nidogen - coiled-coil domain (three chains are wrapped around each other)
- carboxylic end (allows binding to integrins, dystroglycan, perlecan)
At the N terminus all the chains have Globular Regions
*Q: What causes congenital muscular dystrophy? When are symptoms evident from? Symptoms are?
A: Absence of alpha 2 in laminin 2 caused by mutation
birth
- Hypotonia: abnormally decreased muscle tension
- general weakness
- Deformities of the joints
*Q: What are fibronectins? Where is it not found? Can exist as? (2) Interactions?
A: family of closely related glycoproteins of ECM and body fluids // major connective tissue glycoprotein
NOT found in basal membranes
Can exist as insoluble fibrillar matrix or soluble plasma protein
LARGE - capable of interacting with cell surface receptors and other matrix molecules eg collagen // Multi-adhesive
Q: Why are fibronectins important?
A: regulating cell adhesion and migration in embryogenesis and tissue repair
wound healing (promotes blood clotting)
Q: What are fibronectins derived from? Mutations?
A: Only derived from ONE GENE - different forms of fibronectin come from different types of mRNA splicing.
NO KNOWN MUTATIONS IN HUMANS - suggests that it is essential for life (wouldn’t be viable if mutation present)
Q: Draw a diagram for a fibronectin molecule and label.
A: -lots of different domains= multiadhesive
-dimer connected by disulphide bridge-> V shape
N N
\ /
1 1
\ /
\ /
2 2
\ /
3 3
\ /
[] []
\ /
|-S-S-|
|-S-S-|
C C
- collagen binding
- integrin binding (includes RGD sequence)
- heparin binding
Q: How are fibronectin and actin related? Draw diagram to represent.
A: Forms a mechanical continuum with the actin cytoskeleton (same orientation)
extracellular fibronectin fibrils (indirectly linked to inside of cells via… intracellular actin stress fibres
integrin receptors at the cell surface provide the linkage between the matrix and cytoskeleton
collagen
V (fibronectin)
integrin
plasma membrane
other side of integrin
adapter protein
actin filament
Q: How does fibronectin bind to integrin?
A: via RGD molecules on fibronectin
Integrin binds to the RGD sequence which is on the cell binding site
Integrins recognise the RGD motif
Q: Describe the RGD sequence.
A: loop of the integrin binding region
*Q: What are proteoglycans? Structure? Size is determined by? Key Property?
A: type of glycoprotein
- CORE PROTEIN
- one or more GLYCOSAMINOGLYCAN (GAG) CHAINS are covalently attached
- Small proteoglycans have one GAG chain where as large ones can carry around 100 GAG chains (GAGs occupy a large volume relative to their mass)
resistant to compression
Q: What is the structure of GAG chains? Charge? Property?
A: -GAG chains are long, unbranched sugars consisting of a REPEATING DISACCHARIDE
-One of the two sugars in the repeating disaccharide is always an amino sugar
- Highly Negatively Charged - many GAGs are sulfated or carboxylated
- GAGs form hydrated gels which can be very resistant to compression
*Q: What are the families that proteoglycans are categorised into based on? What are the 4 families?
A: structural and functional characteristics
- Basement Membrane e.g. perlecan
- Aggregating (interact with hyaluron) e.g. aggrecan in cartilage
- Small Leucine-Rich e.g. decorin
- Cell Surface e.g. syndecans 1-4 (not part of ECM)
Q: Name 4 main groups of GAG chains.
A: -Hyaluron
- Chondroitin Sulfate/Dermatan Sulfate
- Heparan Sulfate
- Keratan Sulfate
*Q: Give 3 examples of GAG chains on proteoglycans.
A: decorin: single GAG chain
/
/
n
C C
syndecan: 3
N
------|
------|------
|
PM==|=== (transmembrane part)
\ /
C (cystolic region)
aggrecan: 100s
||||| ||||||||||||||||||||||||||||||||
N———————————–C
||||| ||||||||||||||||||||||||||||||||
Q: What connects GAG chains and the core protein?
A: LINK TETRASACCHARIDE
xylose-galactose-galactose-glucuronic acid
Q: What is hyaluron also called? Why is it unique? Where is it synthesised? Size?
A: -hyaluronic acid.
- NO CORE PROTEIN - it only has a carbohydrate chain (not proteoglycan)
- Synthesised in the cell surface - NOT in the ER/Golgi
-Hyaluron is a HUGE molecule which occupies about the same volume as a bacterium.
Q: What’s the structure of hyaluron? (3)
A: -Unsulfated
- contains lots of carboxyl groups
- A single long chain has up to 25,000 repeat disaccharides
*Q: What’s the structure of Dermatan Sulfate?
A: glycosaminoglycan /GAG
C=iduronic acid, S= N-acetylgalactosamine-4-sulfate
carboxyl and sulphate repeating disaccharide (makes it negatively charged)
*Q: What’s the structure of Chondroitin Sulfate?
A: glycosaminoglycan /GAG
C=glucuronic acid, S= N-acetylgalactosamine-4-sulfate
carboxyl and sulphate repeating disaccharide (makes it negatively charged)
Q: What is decorin? Binds to? Mice that can’t produce have? Regulates?
A: -Small proteoglycan
- Binds to collagen fibres
- Mice who cannot make decorin have fragile skin and reduced tensile strength (collagen hasn’t formed correctly)
- Regulates collagen fibre size and arrangement (essential for fibre formation)
