Expression of recombinant human Met-ase-1: a NK cell-specific granzyme

Human Met-ase-1 is a member of a family of cytotoxic lymphocyte serine proteases (granzymes), but is expressed specifically in CD3- large granular lymphocytes with natural killer cell activity. We have devised a polymerase chain reaction strategy to delete the predicted hexapropeptide of human Met-ase-1 (Ser-6 to Gln-1), to enable its expression and activation in mammalian COS cells. In addition, using peptide immunization we have derived a unique and specific monoclonal antibody detecting human Met-ase-1. Western blot analysis and protease assays of transfected COS cell lysates against a panel of thiobenzyl ester substrates formally demonstrated that the human Met-ase-1 gene encodes a serine proteinase that specifically hydrolyzes substrates containing a methionine (Met-) side chain at P1. The expression of active human Met-ase-1 and the generation of a specific anti-human Met-ase-1 monoclonal antibody will now enable a detailed structure/function analysis of key amino acids that confer this unusual serine protease specificity.