Multiple Choice
An α-helix would be destabilized most by:
4. Protein Structure
Alpha Helix Disruption
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Why does poly-L-Glutamate adopt an α-helical structure at low pH but a random conformation above pH 5?
A
Positively charged residues destabilize α-helices.
B
At high pH, the (-) Glu repulsion destabilizes α-helices.
C
Negatively charged residues destabilize α-helices.
D
< pH 5, the (+) Glu repulsion destabilizes α-helices.
Verified step by step guidance1
Understand the structure of poly-L-Glutamate: It is a polymer composed of glutamate residues, which have a carboxyl group in their side chain that can be protonated or deprotonated depending on the pH.
At low pH (below 5), the carboxyl groups in the side chains of glutamate residues are protonated, resulting in a neutral charge. This lack of charge allows the poly-L-Glutamate to adopt an α-helical structure because there is no electrostatic repulsion between the side chains.
As the pH increases above 5, the carboxyl groups become deprotonated, resulting in negatively charged glutamate residues. This introduces electrostatic repulsion between the negatively charged side chains, destabilizing the α-helical structure.
The destabilization of the α-helix at higher pH is due to the repulsion between the negatively charged glutamate residues, which prevents the close packing of the helix and leads to a random coil conformation.
In summary, the α-helical structure of poly-L-Glutamate is stable at low pH due to the lack of charge repulsion, while at high pH, the negative charges on the glutamate residues cause repulsion that destabilizes the helix, leading to a random conformation.
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