Insulin has two confromational states, and the main difference in the B chain (t

Question

Insulin has two confromational states, and the main difference in the B chain (the long chain) between the two states is the lenght of the central alpha-helix.In the more relaxed state, the helix extends from 3 to residue 19, while in the other state the helix only extends from residue 8 to residue 19.

1). Given the parameters of an alpha-helix, what is difference in lenght of this central helix between the two confromations of Insulin?

2). How many more turns of the helix are in the relaxed conformation?

3). Insulin is stored in the pancreas as an inactive hexamer, and released to the blood stream as an active hormone in monomer form. The conformational states described above are thought to be essential for the transition from hexamer to monomer. The relaxed state appears to be preferred for hexamer formation. As a budding young biochemist, briefly hypothesize why the conformational change might cause a change in the quaternary structure.

Explanation / Answer

Ans 1

Rise of helix per amino acid in right handed form is 1.5Ao.

Therefore, in first case, length will be =19-3*1.5=24 Ao

Likewise, length of cylinder in second case will be =19-8*1.5=16.5 Ao

Ans 2

There would be very faint chance to formation of any additional helix in this case.

Ans 3

The quaternary structure of protein is basically defined by the proximity of functional groups present in the secondary structure of polypeptides. Thus, the alteration in secondary structure may cause the alterations in the distance of functional groups, which in turn may cause the variation in various types of interactions, like hydrophobic-hydrophobic interaction, hydrophilic hydrophobic interactions, electrostatic interactions and most importantly, formations of di-sulfide bond.

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