Question

Papain is a cysteine protese from the papaya plant. It is commonly used for breaking down protein deposits that build up on contact lenses. Instead of having a catalytic triad like in serine protease and hydrolyases, it has a catalytic dyad comprised of cysteine and a histidine with an asparagine assisting in catalysis.

a) Propose a mechanism for the hydrolysis of a peptide by pepain.

b) Why is cysteine more nucleophilic than serine?

c) Why might C1 be even more nucleophilic than a typical cysteine?

Answer 1