CSB327 Lecture 18 Summary

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University of Toronto St. George
Cell and Systems Biology
Maurice Ringuette

Lecture 18 - Structure of artery o Endothelium  Basal lamina  Elastin  Smooth muscle  Elastic connective tissue  Epithelium - Elastin o Broadly distributed o Laterally packed o Thin order filaments o Fenestrated o Pores allow exchange of nutrients and metabolites o Provides elasticity and resilience to connective tissues o Complements with collagen fibrils, which provide tensile strength o Permits long-range deformability and passive recoil o Dense rope-like network o Half-life is 70 years  Various enzymes (MMPs and serine proteases) and UV light are able to cleave or damage elastic fiber molecules o Elastin network has repeated cycles of extension and recoil o Elastin molecules are linked together by LOX o Recoil without input of energy because driven by entropy  In stretched state, the water is organized (low entropy)  In the recoiled or relax state, the water is disorganized (high entropy) - Coacervation of tropoelastin (phase separation and aggregation of TE) o Endothermic, entropy driven process o Caused by multiple interactions of individual hydrophobic domains o Inverse temperature solubility  Change in temperature, pH, hydration, or salts (ionic strength) will force TE out of solution  Increasing the temperature will force TE out of solution  Decreasing the temperature makes TE soluble in aqueous solutions  Hydrated TE decreases the temperature at which coacervation can occur  Interaction of hydrophobic domains o Phase separation - Structure of tropoelastin o Alternating hydrophobic domains and cross-linking domains o No evidence of glycosylation o Single copy gene o Soluble precursor o Found in all vertebrates o Appearance coincident with the formation of a closed circulatory system o Interacts with fibrillin o Synthesized by smooth muscle cells, endothelial cells, chondrocytes and fibroblasts (SCEF) o Rich in hydrophobic residues (Pro, Gly, Ala, Val) o Since there are no internal Met residues (signal peptide was cleaved), elastin can be purified by digesting connective tissue with CnBr - Molecular organization of tropoelastin o Hydrophobic domains (beta sheets)  important for assembly and elasticity  Large hydrophobic side chains above and below the plane of the beta sheet  Rich in Gly, Pro, Ala, Val (GPAV) o Cross-linking domains (Lys)  important for stability  Stretches of Lys separated by two or three Ala residues  LOX cross-links Lys  Forms desmosine and isodesmosine tetrafunctional cross-links of elastin  Unique to elastin  Tetrafunctional cross-links (desmosine and isodesmosine) by LOX - Fibrillin-1 o Neuraminidase remove sialic acid residues from sialoglycoproteins to expose galactose on fibrillin o Neur1-null  Decreased elastin content (e.g., thinner and irregularly shaped)  Abnormal separation between elastin lamina
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