Question

Why is substitution of a Pro amino acid in the middle of an alpha-helix always disruptive?

Answer 1

The primary structure of a protein is a linear polymer with a series of amino acids. These amino acids are connected by C-N bonds, also known as peptide bonds. The formation of peptide bonds produce water molecules as a by-product when an amino terminal residue (N-terminal) loses an oxygen from the alpha-carboxyl group while the other amino acid loses two of its hydrogens from its alpha-amino group. Thus, polypeptide, or polypeptide chain, is a term that describes the multiple connected peptide bonds between numerous amino acids. Each amino acid in a polypeptide chain is a unit, commonly known as a residue. These chains have a planar backbone, as the peptide bonds have double bond characteristics due to the existence of resonance between the carbonyl carbon and the nitrogen where the peptide bonds form. The primary structure of each protein has been precisely determined by the specific genes. The C-N bond in an amino acids chain has the character of a double bond. This bond has a short length and stable. It cannot be rotated. This double-bond character can be explained structurally, in that the R groups in amino acid chains avoid steric clash.

Amino acids are linked by peptide bonds to form polypeptide chain; each amino acid unit is known as a residue; a polypeptide chain constructed by the same unit is known as the main chain or backbone and a changing R group, side chains.