ECM II Flashcards
what are glycoconjugates
are proteins or lipids that contain covalently linked glycan (sugar) chains
name 2 glycans in glycoconjugates
oligosaccharides and GAG
what is a glycoprotein
oligosaccharide chains attached to a protein core
what is a glycolipid
membrane lipid whose polar head is modified with oligosaccharides
what are proteoglycans
a core protein linked to many GAG chains. Use the bottle brush model
what are the 2 types of linkages that can be present in glycoproteins
N-
O- glycosidic linkages
where is the N-glycosidic bond
between N-acetylglucosamine and the NH2 in the side chain of an Asn residue
the core of N linked glycoproteins is called a
chitobiose: made of 3 mannose and 2 N acetylglucosamine
3 steps of c-post-translational processing of N-linked glycoproteins
- they have a specific motif that is read by glycosylation machinery (this performs the initial glycosylation process while its being synthesized in the RER)
- oligosaccharides are attached
- processing in the ER, golgi and then attachment of other monosaccharides
where is the O glycosidic bond
between Xyl, Gal, GalNAc and the OH on the side chain of Ser/Thr residue
name 2 O-linked core sugars
- xylosyl serine
- galactosyl hydroxylysine
as oligosaccharides are
c mobile, give examples of their different conformations
erythrocyte glycocalyx - helps antigen blood recognition and flowing through small capillaries
what are GAG
long carbohydrate polymers made of repeating disaccharide units. Are -vely charged due to sulfate and uronic acid groups.
the major monosaccharide components of GAG are
- amino sugars
- uronic acids
where is hyaluronic acid found
joints and ocular fluids
where is chondroitin sulfate found
cartilage, tendons, bone
where is dermatan sulfate found
skin, valves, blood vessels
where is heparan sulfate found
cell surfaces
where is heparin found
mast cells, liver
where is keratan sulfate found
cartilage cornea
how are GAG attached to the core protein
all (except hyaluronic acid) attach to Ser/Thr residue via Gal-Gal-Xyl
keratan sulfate is both free and bound. KS I is N linked, KS II is O-linked
how are proteoglycans degraded
in lysosomes.
protein core is hydrolysed by proteases, GAG are degraded by acid hydrolases
what are the functions of proteoglycans
Occupy space between cells and collagen
Organize water molecules
• Highly viscous - lubricating fluid in the joints
• Specific binding to other macromolecules
• Associate with collagen fibers - network - in the bone, combine with calcium salts (calcium carbonate, hydroxyapatite)
• Anchoring of cells to matrix fibers
• Cell migration and adhesion
ECM structural glycoproteins function to?
bind collagens, proteoglycans and cells
are fibronectin and laminin
give 4 characteristics of fibronectin
- is a high weight glycoprotein
- binds to integrins
- cellular fibronectin produced by fibroblasts is assembled into insoluble fibrils
- plasma fibronectin produced by hepatocytes circulates in a soluble form
explain the structure of fibronectin
- dimer : due to disulfide bonds at C terminal
- string of beads appearance
functions of fibronectin
- cell adhesion, differentiation, growth, migration
- anchoring basal lamina to ECM parts
- coagulation
- embryogenesis
- metastasis
how are fibronectin fibrils formed
- soluble fibronectin binds integrins
- this binding induces reorganization of actin filaments and signaling
- cell contractiliy leads to changes i FN formation, forming fibrls
give 4 charcteristics of laminin
- high weight glycoprotein
- heterotrimeric
- undergo reversible self association to form polymers in Ca presence
- interacts with integrins via multiple binding sites
- binds ECM components, including heparan sulfate (directly), and collagen IV (mostly indirectly via nidogen/entactin)
3 functions of laminin
- cell adhesion
- cell differentiation
- conjunction with entactin, LN generates a scaffold for anchoring of cells and ECM molecules in the basement membrane
give 4 characteristics of integrins
- adhesion molecules
- can transduce signals from ECM leading to change in cell morphology
- need to be activated by inside-out signaling
myosin light chain phosphorylation is mediated by
Rho
