C. The micellar structures of exon 3 (shown above) are able to assemble into pol

Question

C. The micellar structures of exon 3 (shown above) are able to assemble into polymers when exon 3 is isolated from the other exons. The size and organization of the micellar polymers is more random in water, though the polymer does still form when water is present. Upon heating exon 3 micellar structures themselves become more organized and the polymer becomes more tightly organized as well. These polymer structures are shown below (each circle is one of the micellar structures on the left -ignore the red). Rs Micellar polymer How might this behavior of resilin, in vitro, give us a model for its 'elasticity' in vivo? Explain how the looser water-containing structure and the tighter water- excluding structure may give us a general mechanism for the elasticity of biological proteins.

Explanation / Answer

Elasticity is a physical attribute, which defines an intrinsic ability of a material to get back to its original shape after getting deformed by the action of an external force. Elastomeric proteins are those proteins which posses elasticity. These proteins are special because they contain independent, conformation-free and flexible monomeric chains that are cross-linked at specific points to ensure re-coil.

One such rubber-like elastomeric protein is resilin. These are superelastic rubbers found in the flight and jumping organs of the insects because of the extreme need for cyclic extension and retraction. During experimental studies by Anderson, the first intermolecular crosslinks identified were di and tri tyrosine from resilin protein. In Drosophila, full-length resilin structure has three domains as exon1, exon2 , and exon3. Resilin is a hydrogel, that is when with water it becomes swollen. (looser water-containing structure). In the absence of water, resilin acts like a glass-polymer. (tighter water excluding structure). In the given question, on altering the hydration levels of resilin, the elasticity is also affected. Dehydration decrease the core elasticity and rubber properties of resilin. This is because water acts as a plasticizer for the cross-linking network in resilin by increasing the hydrogen bonding. Also, other factors like the high concentration of specific amino acids like glycine and proline, polyproline helices and hydrophilic regions serve for increasing water content in the resilin protein network. This phase separation leading to looser water-containing structure and tighter water-excluding structure explains the physical feature of elasticity in biological proteins.

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