BCHM 2021 Lecture Notes - Lecture 9: Dermatan Sulfate, Keratan Sulfate, Heparan Sulfate

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BCHM2021 Lecture 9: Chapter 19
Cadherins: Ca2+-dependent adherins
Classical: E-cadherins (endothelial), N-cadherins (neural), P-cadherins (placental)
Nonclassical: protocadherins, desmosomal, unconventional,
cadherin junctions: homophilic (like-to-like)
*Spacing is dependent on cadherins.
Extracellular cadherin domains (EC domains)
N-terminal domains
Ca2+ binding prevents flexing and creates a curved rod, shape: (>1mM) (<0.05mM = no
binding)
Components (different domains)
Extracellular: homophilic
Intracellular: cytoplasmic interaction (actin/desmosomes)
a) Β-catenin
b) p120-catenin
Mechanotransduction
Stretch of α-catenin due to cell tension sensed by actin-myosin complex
oallows vinculin to bind (which allows more actin filaments to interact)
oPulling: increases contractile force
Zonula adherens (adhesion belt): interacts with bundles of actin filaments
Desmosomes
Intracellular Cell-to-cell junction made of Cadherins interacting with intermediate
filaments.
Provides mechanical strength
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Also called macula adherens or “adhering spot”
Dense plaque of adaptor proteins
Desmosomal cadherins
a) Desmoglein
b) Desmocolin: which binds to:
i. Plakoglobin (related to β-catenin)
ii. Plakophilin (related to p120-catenin)
*both bind to desmoplakin for intermediate filaments
Tight Junctions
1. Restricts membrane proteins & lipid movement
2. Restricts Extracellular molecule movement
3. Formed by transmembrane proteins
a) Claudin: resposnible for asssembly
b) Occludin: responsibe for acting as a barrier
*claudin-claudin & occludin-occludin interaction
c) tricellulin: helps seal the two membranes together
Gap Junctions
Connect adjacent cells (permeable to small soluble molecules)
Formed by the proteins:
a) Connexins: for vertebrates
b) Innexins: for invertebrates
Small inorganic ions and small water-soluble molecule (800-1000 daltons) purely passive
move through
Vertebrates contain 2 connexons: each made up of 6 connexins
Connexins are either homomeric, forming homotypic gap junctions by homomeric +
homomeric dimers, or heteromeric, forming heterotypic gap junctions by homomeric +
heteromeric dimers
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Plants
Pectin (a polysaccharide): important for extracellular communication, due to rigid plants walls
compared to plasma membrane
Called plasmodesmata (continuous between cells) that have desmotubule; centre of
plasmodesmata
Connected to smooth endoplasmic reticulum at both cells
Movement of <800 daltons
Cell-cell adhesion proteins
a) Selectins: carbohydrate-binding proteins
b) Integrins
c) Immunoglobulin (Ig superfamily)
Selectin structure
a) Extracellular lectin domain
b) EGF-like domain
c) Single transmembrane domain
d) Intracellular domain: anchoring domains (more actin)
3Types of Selectin found that can be found in the bloodstream
1. L-selectins (lymphocytes)
2. P-selectins (platelets & endothelial)
3. E-selectins (endothelial)
Inflammation: P- selectin and E-selectin are produced to bind WBC (initial weak bind)
Integrins then bind o Ig superfamily proteins from lymphocytes (secondary strong bind)
Selectin-integrin adhesion: heterophilic
Endothelial Ig superfamily proteins
1. ICAM – Intracellular adhesion molecule
2. VCAM – vascular cell adhesion molecule
*both are heterophilic
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