Molecular cloning and localization of a novel serine protease from the colonial tunicate Botryllus schlosseri

A cDNA encoding a putative serine protease was isolated and characterized from Botryllus schlosseri, a colonial protochordate. The open-reading frame of the 846 bp cDNA is 744-nt long. The deduced aa sequence predicts a protein of 26,134 D, with the signature of chymotrypsin. The mRNA of the protease is expressed only in the zooids as a single 0.9-kb transcript. No transcript was found in the tunic matrix (test). Surprisingly, a 3.7-fold higher enzyme activity was found in the test, compared with the zooids. We propose that this serine protease may have a role as a biologically active compound in the defense mechanisms against epibionts or as part of the effector mechanisms expressed in allogeneic and xenogeneic interactions.