Increasing the thermal stability of euphauserase - A cold-active and multifunctional serine protease from Antarctic krill

A molecular model of Antarctic krill euphauserase based on the known crysta l structure of its fiddler crab analog, collagenase I, indicates that the c ore structure of these enzymes is almost identical. Euphauserase is a cold- active and thermally sensitive enzyme with a high affinity for Lys, Arg and large hydrophobic amino acids. Residue Phe137 in euphauserase, localized i n loop D (autolysis loop), is highly exposed on the surface of the molecule . Therefore, it appeared to be an easy target for autolysis. The broadly sp ecific euphauserase has a low affinity for negatively charged residues. In order to increase the stability of the enzyme, two mutants were created in which residue Phe137 was replaced by a Glu and an Asp residue. Both mutatio ns resulted in increased stability of the recombinant euphauserase towards thermal inactivation.