Question

16. When a Cys residue in a protein is mutated to Asp, the protein loses its function. Which is the least likely explanation? A. The protein is part of ESCRT-O and therefore requires a disulfide bond at the Cys for stability. B. The protein is a Rab and the Cys is in a Caax prenylation motif. C. The protein is an E2 ubiquitin conjugating enzyme and the Cys is the attachment site for ubiquitin. D. The Cys is part of an HSP70 binding site, and the Asp prevents HSP70 binding and therefore interferes with folding. E. The Cys normally becomes the N-terminal residue after cleavage of the protein, and having Asp as the N-terminal residue causes N-end rule degradation.

Answer 1

When a Cys residue in a protein is mutated to Asp, the protein loses its function. The answer for this question would be A

A: The protein is a part of ESCRT-O and therefore requires a disulfide bond at the cys for the stabilty.

Explanation:

As we know the structure of Cys residue, it has a thiol group (-SH) and the probable function would be disulfide bond formation.

If mutation in protein from Cys to Asp resulted loss of function of protein, the reason could be disulfide bond required for its stability of protein.