麻省理工大学：《生物材料——组织交互作用》教学讲义（英文版）The Extracellular Matrices Part

The Extracellular Matrices Part l 2. Elastin fibers 3. Proteoglycans(PG)and glycosaminoglycans (GAG) 4. Cell-adhesion molecules(CAM)

The Extracellular Matrices Part II. 2. Elastin fibers. 3. Proteoglycans (PG) and glycosaminoglycans (GAG). 4. Cell-adhesion molecules (CAM). 1

Elastin fibers A network of randomly coiled macromolecules No periodicity. Highly extensible chains. Rubber-like elasticity is complicated by ydrophobic bonding effects Interaction of hy drophobic(nonpolar)aa with water leads to hydrophobic bonding. Primarily entropic, not energetic, bonding between molecules. It forces nonpolar macromolecules, such as elastin, to adopt a compact, rather then extended shape in hydrated tissue Stretching of elastin fibers leads to large entropy loss due to reduction in chain configurations and increased"ordering"of water molecules against nonpolar AA. spontaneous retraction Elastic ligament of neck, blood vessel wall

Elastin fibers • A network of randomly coiled macromolecules. No periodicity. Highly extensible chains. • Rubber-like elasticity is complicated by hydrophobic bonding effects. • Interaction of hydrophobic (nonpolar) AA with water leads to hydrophobic bonding. Primarily entropic, not energetic, bonding between molecules. It forces nonpolar macromolecules, such as elastin, to adopt a compact, rather then extended, shape in hydrated tissue. • Stretching of elastin fibers leads to large entropy loss due to reduction in chain configurations and increased “ordering” of water molecules against nonpolar AA. Spontaneous retraction. • Elastic ligament of neck. Blood vessel wall. 2

The Hydrophobic bond △G=△H-T△S Equilibrium when AG =0. G is Gibbs' free energy, the enthalpy is H=E+ pv, t is absolute temperature and s is the entropy. The process goes spontaneously from left to right when AG Ch in Ho The experimental data show (all units in calories per mo):△G=△H-T△s +2600=-2800-298(-18 +2600=-2800+5400 Conclusion: Insolubility of paraffin in water due to entropy loss, not to enthalpy change!( Kauzmann)

The Hydrophobic bond 3 ∆ G = ∆ H − T ∆ S Equilibrium when ∆ G = 0. G is Gibbs’ free energy, the enthalpy is H = E + PV, T is absolute temperature and S is the entropy. The process goes spontaneously from left to right when ∆ G < 0. Find the position of thermodynamic equilibrium for a well-known example of insolubility: CH 4 in benzene → CH 4 in H 2 O The experimental data show (all units in calories per mol): ∆G = ∆ H − T ∆ S +2600 = −2800 − 298 ( −18 ) +2600 = −2800 + 5400 Conclusion: Insolubility of paraffin in water due to entropy loss, not to enthalpy change! (Kauzmann)

Historical models of cell membrane structure Image removed due to copyright considerations

Historical models of cell membrane structure Image removed due to c Image removed due to copyri opyright consi ght considderati eratioons ns 4

Cell membrane showing Extracellular bilayer Oligosaccharide Glycoprotein Peripheral Glycolipid rotein structure Integral c Hydrope Intracellular

Cell membrane showing bilayer structure 5

Elastin fibers in the relaxed aorta Elastin macromolecules are random coils tied together to form a 3-dimensional (insoluble)network Images removed due to copyright considerations Macromolecules coil upon themselves due to high content of nonpolar(hydrophobic) amino acids that mediate withdrawal from polar medium (aqueous buffer) and promote bonding within chains. These networks stretch extensively like all rubbers

Elastin fibers in the relaxed aorta. Elastin macromolecules are random coils tied together to form a 3-dimensional (insoluble) network. Images removed due to Images removed due to copyright consi copyright considderations erations Macromolecules coil upon themselves due to high content of nonpolar (hydrophobic) amino acids that mediate withdrawal from polar medium (aqueous buffer) and promote bonding within chains. These networks stretch extensively like all rubbers. 6

Proteoglycans(PGs)and glycosaminoglycansGAGs a proteoglycan is a poly peptide chain(proteo) with polysaccharide(glycan or GAG)side chains Primary structure modeled as an alternating copolymer of two different glucose-like units, one of them an acidic sugar-like molecule the other an amino sugar with a negatively charged sulfate group (except hyaluronic acid that is not sulfated) Electrostatic interactions between charged groups in GAG side chains of PG responsible for about 50% of stiffness of articular cartilage(Grodzinsky et al.)

Proteoglycans (PGs) and glycosaminoglycans (GAGs) • A proteoglycan is a polypeptide chain (proteo) with polysaccharide (glycan or GAG) side chains. • Primary structure modeled as an alternating copolymer of two different glucose-like units, one of them an acidic sugar-like molecule, the other an amino sugar with a negatively charged sulfate group (except hyaluronic acid that is not sulfated). • Electrostatic interactions between charged groups in GAG side chains of PG responsible for about 50% of stiffness of articular cartilage (Grodzinsky et al.). 7

Proteoglycans(PGs)and glycosaminoglycans(GAGs) Images removed due to copyright considerations

Proteoglycans (PGs) and glycosaminoglycans (GAGs) Images removed due to Images removed due to copyright consi copyright considderations erations 8

Glycosamine Image removed due to copyright considerations glycans Diagram of Chondroitin 4-Sulfate Image removed due to copyright considerations. disaccharide repeat unit Diagram of dermatan Sulfate Image removed due to copyright considerations Diagram of Heparan Sulfate

9 Γλυκοσαµινογλυκανες Glycosamino￾glycans disaccharide repeat unit Image removed due to copyright considerations. Diagram of Chondroitin 4-Sulfate Image removed due to copyright considerations. Diagram of Dermatan Sulfate. Image removed due to copyright considerations. Diagram of Heparan Sulfate

Proteoglycans and glycosaminoglycans repeat unit of chondroitin 6-sulfate Image removed due to copyright considerations a proteoglycan 10

10 Proteoglycans andΓλυgκοlycosaminoglycans σαµινογλυκανες repeat unit of chondroitin 6-sulfate a proteoglycan Image removed due to copyright considerations