Question

which of the following altrations of protein structure would have least affect on the ability of a protein to function as an enzyme?
a) alkylation of single Cys residue of protine with iodoacetate.

b)site-directed mutagenesis in which an Ile in the interior of the protein is replaced by a V al

c) Amidation of all Glu to Gln

d) faliure to remove the N- terminal hydrophobic peptide of all protein during processing

Answer 1

b. substitution I->V is less likely to affect enzymatic activity. Residue located interior globe is involved in formation of hydrophobic core. Change of one hydrophobic side chain to another one should not affect structure and stability of the protein significantly. Cysteines are located within catalytic center of enzymes and there modification could be critical for enzymatic activity. Amidation of Glu causes loss of charge this might impact on catalytic center, allosteric regulation and stability as well.