Biochemistry—Protease Specificity Rules What peptide bond specificity is characteristic of the protease clostripain?

Introduction / Context:
Different proteases display distinct primary specificities, recognizing particular side chains near the scissile bond. Knowing these rules allows prediction of fragment patterns after digestion and informs protein sequencing strategies.

Given Data / Assumptions:

• Clostripain is a protease from Clostridium species.
• Primary specificity distinguishes it from trypsin and other proteases.
• We focus on the residue on the P1 side of the cleavage site.

Concept / Approach:
Recall canonical specificities: trypsin cleaves after lysine or arginine (with context effects), while clostripain shows strong preference for cleavage after arginine specifically. Therefore, among the options, the correct description is cleavage on the carboxyl side of arginine residues.

Step-by-Step Solution:

Verification / Alternative check:
Empirical digests and proteomic mapping consistently show Arg-specific cleavage patterns for clostripain under standard conditions.

Why Other Options Are Wrong:

• After His or after Lys: not the hallmark specificity of clostripain.
• “None of the above”: incorrect because Arg specificity is well established.
• Before Arg: incorrect side of cleavage for the described enzyme.

Common Pitfalls:
Confusing clostripain with trypsin; mixing up “before” versus “after” nomenclature when describing cleavage sites.

Final Answer:
It cleaves on the carboxyl side (after) arginine residues