Question

Based on the structure of individual keratin subunits, why would a single point mutation in the alpha-helical region of the monomer result in a defect in the polymer? Be sure to explain it from the standpoint of DNA and intermediate filament structure.

Answer 1

The point mutation in keratin is an example of cytoskeleton disorders. α-keratin is a fibrous structural protein, made up of amino acids that form a repeating secondary structure and this secondary structure forms a coiled coil. Through disulfide bonds, they form a protofilament and the two protofilaments aggregate to form a protofibril, and four protofibrils polymerize to form the intermediate filament and this filament is the basic subunit of α-keratins Keratin serves as structural and protective functions, particularly in the epithelium.

The point mutation is a genetic mutation, in which a single nucleotide base in DNA sequence is changed and this mutation in DNA alters the mRNA and thereby alters the amino acid chain. As a result, wrong amino acid getting produced, which alters the protein and this cause problems to the polymeric protein structure.

The single point mutation in polypeptide chains affect the twisting and thereby effect the formation of left-handed helical structure known as a coiled coil. The point mutation in α-keratin thereby affect it's functions.