Earthworm-serine protease: Characterization, molecular cloning, and application of the catalytic functions

An earthworm, Lumbricus rubellus, produces alkaline serine proteases that are greater than trypsins in their activity and stability. The proteases which were purified from the earthworm were composed of six isozyme proteins. Each isozyme consisted of a single polypeptide chain which was derived from the different genes. The enzymes had activity and were stable at below 60°C over a wide range of pH 2-11 and were strongly resistant to organic solvents and detergents. Moreover, they retain full activity for long years at room temperature. They acted on various proteins, such as elastin as well as fibrin, and some peptides, such as β-amyloid 1-40 and solubilized actual fibrin clots of whole blood in a rat's vena cava. They also catalyzed the hydrolysis of various esters. The cDNAs encoding the proteases were cloned and sequenced. They showed similarity to mammalian serine proteases and conserved the catalytic amino acid residues, however, neither arginine nor lysine residues were present in the autolysis region. The gene encoding the native form of an isozyme protein was expressed in Pichia pastoris to produce the active protease in the culture medium. The proteases contributed to the production of the "earthworm autolysate". The extracts of the autolysate could be used as a "peptone substitute" in media for the efficient growth of microorganisms.