there are also some critical residues including pro 164 which help bend the peptide backbone of the glu163 to offer the correct geometry so the catalytic process can occur. cis-proline on the other hand offers dimer stability. the ns2-3 protease requires both ns2 and ns3 domain for proteolytic cleavage. addition of zinc is also required as ns2-3 protease is zinc dependent which releases n terminus of ns2. the tetrahedral geometry in active site hints at the zinc ion binding site. although ns3 domain's active role is not known yet, scientist propose that ns3 may interact with the active site of ns2 which would provided with catalytic environment necessary for polyprotein processing. the presence of zinc-binding site doesn't necessarily mean that a devoid of zinc in the process would inhibit the viral catalytic process.