Question

Protein Z is a protein which is phosphorylated at Ser-120. The functional role of this phosphorylation site

in protein Z was assessed by site-directed mutagenesis. Mutation of Ser-120 to Asp resulted in a protein that

is unable to function, while mutation to Ala resulted in a protein with increased ability to function. Discuss a

structural basis for these observations.

Answer 1

Majority of the proteins are phosphorylated and regulates its function. The most common phosphorylated amino acid in protein are serine, threonine, and tyrosine. The phosphorylation of amino acid residue introduces a charge in the protein, making a hydrophilic in nature which alters the interaction of that protein with nearby proteins. The addition of a phosphate group in non-charged amino acids can result in the alteration of a hydrophobic region of the protein into an extremely hydrophilic portion of the protein. Therefoer, the protein dynamics can result in a conformational change in the structure of the protein and thereby regulating the function.

In the given observation, first Ser-120, the site for phosphorylation is mutated into Asp, which contains -COOH as R group. The conversion of the Ser to Asp can result in no change in charge of the region. however, mutation of Ser to Ala, a non-charged amino acid will result in the conversion of the hydrophilic site as hydrophobic resulting in an alteration of protein function.