Question

What would be the effect of a mutation that replaced the alanine residue at point A in the structure with a threonine residue?

- This would not affect the molecule and the mutant protein would be functional.

- This would break the helix and form hairpin structures, that would make the mutant protein nonfunctional.

- This would result in a partially unfolded protein, and the mutant protein would be nonfunctional.

- This would break the helix near the Fe₂ binding sites, and the mutant protein would change functions.

- This would break the helix near the binding sites and Fe₂ could not be bound, and the mutant protein would be nonfunctional.

(The last option is not correct)

Please give an explanation as to why as well :)

Answer 1

Option "B" is correct. Generally, the alpha -helix is considered as a native structure of polypeptide chain but substitution of few amino acid may disrupt alpha-helix structure and may convert these structure to beta strand,loop or turns depending on the amino acid substituted. Thus, the mutation in amino acid of a protein from alanine to threonine will affect the structure and function of protein because threonine , being more polar, larger in size with two non hydrogen substituent attached to the branched beta carbon adds bulkiness near the polypeptide backbone making it difficult for the protein to adopt alpha helical structure and preferring beta sheet.