Which event could alter a protein's primary structure?A.Site-directed mutagenesis of the gene that encodes the proteinB.A conformational change in the protein induced by ligand bindingC.Protein denaturation by guanidinium chlorideD.Reduction of disulfide bonds by β-mercaptoethanol

The event that could alter a protein's primary structure is A. Site-directed mutagenesis of the gene that encodes the protein.

Here's why:

A. Site-directed mutagenesis of the gene that encodes the protein: This process involves the intentional change of the DNA sequence of a gene, which will subsequently change the amino acid sequence that the gene encodes for. Since the primary structure of a protein is its sequence of amino acids, this process would directly alter the protein's primary structure.

B. A conformational change in the protein induced by ligand binding: This would not alter the primary structure of the protein. It would cause a change in the protein's shape (conformation), but not its amino acid sequence.

C. Protein denaturation by guanidinium chloride: This process disrupts the secondary, tertiary, and quaternary structures of a protein, but not the primary structure. The amino acid sequence (primary structure) remains the same.

D. Reduction of disulfide bonds by β-mercaptoethanol: This process breaks disulfide bonds, which are part of a protein's tertiary structure. It does not change the amino acid sequence, so it does not alter the primary structure.