Exon I 325 387 605 Chiin-binding domain Ctorminal elastic repeat unils Figure 1:

Question

Exon I 325 387 605 Chiin-binding domain Ctorminal elastic repeat unils Figure 1: Resilin- Exons 1, 2 and 3 each comprise separate functional protein domains. Exon i extends out of the cell into the extracellular space and exon 3 is polysaccharide in the membrane that comprises the exoskeleton of insects. Its function is thus to anchor the extra- and intracellular subunits of resilin to the exoskeleton of insects. A. Exon 1, which extends outside of the cell membrane, contains 18 'elastic repeat units' (depicted as yellow disks in Figure 1) which are 15-mer repeats of these amino acids: GGRPSDSYGAPGGGN. These segments are attached by short (2-5) amino acid segments of opposite polarity to the 15-mer repeat units. Additionally, at the N- and C- terminus of this exon are larger segments that also have opposite polarity to the 15-mer repeat. In other words, the blue and yellow regions of exon 1 ih the diagram above have opposite polarity. Exon 1, when studied in isolation, takes an extended conformation in water. In other words, it does not take any secondary structure but retains a mostly disordered structure. Upon heating, or removal of water, individual exon 1 peptides begin to aggregate into stacks, as depicted below. Explain why the protein folds this way with and without water present. You should use your knowledge of amino acids to deduce the polarity of the 15-mer repeat and thus the polarity of the connecting regions. Consider glycine ambivalent in polarity neither polar nor nonpolar.

Explanation / Answer

Ans. Hydration of protein is very important for its 3D structure, the dynamic conformation and activity of the protein molecule. The aqueous structuring of water molecules around proteins affects out at least 1-1.5nm from its surface to 2-3nm between neighbouring proteins.

The structure and dynamics of the hydration layers in the protein are affected by the protein surface composition(hydrophobic, polar, hydrogen bonding, acidic and basic groups present). Hydration is slower near hydrophobic groups than near hydrophilic residues.

The relative hydrophobicities order:

D<E<K<R<Q<H<N<S<Y<W<T<M<F<C<G<A<I<V<L<P.

Water molecules arrange themselves around protein and forms gradient which affects the activity of the molevule and also leads to small empty spaces(also called dehydrons).

And when we heat it causes the removal of water molecules which leads to shrinkage or coagulation of protein for eg in egg when we heat it, their protein molecule start losing its original conformation and become coagulate.

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