Molecular modelling of king crab, salmon, and bovine trypsin. a – c: Electrostatic surfaces of (A) king crab trypsin (homology model), (B) bovine trypsin (pdb code: 1s0r), and (C) Atlantic salmon trypsin (pdb code: 1hj8). The most electropositive potential is shown in blue, whereas the most electronegative potential is shown in red. The PAR-2 agonist peptide is displayed in green ribbon. d: The N-terminal fragment of PAR-4 and PAR-2, Arg at the cleavage site (shaded), *: a conserved positive charged residue in tethered peptides. e and f: The location of 3 binding site residues in the king crab trypsin model that corresponds to different residues in the bovine and Atlantic salmon trypsin (shaded boxes in the structural alignment). Asp196 in king crab trypsin corresponds to Met175 in Atlantic salmon and Gln155 in bovine trypsin; Arg244 in the king crab trypsin corresponds to Glu221 in Atlantic salmon and Gln199 in bovine trypsin; and Tyr247 in king crab trypsin corresponds to Asn224 in Atlantic salmon trypsin and to Lys202 in bovine trypsin.