Question

1. When part of a protein chain, the amino acid proline also lacks a backbone hydrogen bond donor; mutations to proline will delete a backbone hydrogen bond. List two reasons why proline mutagenesis is problematic for selectively studying backbone hydrogen bonds.

2. Draw chemical structures for the amino acids or hydroxy acids with these abbreviations: A, α, F, ϕ

3. Draw the structure of one of the 20 canonical amino acids whose side chain contains a hydrogen bond donor group. Propose a structure for an unnatural amino acid (you get to make it up!) to selectively test the effect of weakening or eliminating this hydrogen bonding ability (without dramatically changing the steric bulk or other functional groups on the side chain)

Answer 1

1st qutestion:

Let us first understand the biosynthesis of proline.

Proline is synthesised from glutamic acid by reduction of alpha- carboxyl group to form glutamate semialdehyde. When this semialdehyde group reacts with alpha- amino group results in elimination of an water molecule. followed by reduction step results in synthesis of proline in cyclic form because of lack of back bone hydrogen bond.

Looking at its biosynthesis process proline lacks an alpha amide hydrogen group because of which it brings structural ridgidity to the 3D structure of proteins results in bending of protein of chain.

Mutation in proline can cause destabilization in protein structure by varying the thermodynamics of protein stability by varing hydrophobic intereactions of original residues etc.

2.