2. The following shows the mechanism of a key step of the enzymatic hydrolysis of peptide bonds (amide bonds) catalyzed by cysteine protease. In this step, the side chain of a cysteine (Cys) in the enzyme's active site is deprotonated by the imidazole side chain of an adjacent histidine residue (His). The deprotonation facilitates the formation of the C-S bond between the cysteine and the peptide. peptide X HN X HN R R S side chain of His N-- HS N-H + Cys side chain of Cys -Cys His His (a) What is the role of the side chain of cysteine in this reaction? acid catalyst base catalyst nucleophile electrophile (b)What is the role of the side chain of histidine in this reaction? acid catalyst base catalyst nucleophile electrophile