Characterization of a Novel Serine Protease Inhibitor Gene from a Marine Metagenome

A novel serine protease inhibitor (serpin) gene designated as Spi1C was cloned via the sequenced-based screening of a metagenomic library from uncultured marine microorganisms. The gene had an open reading frame of 642 base pairs, and encoded a 214-amino acid polypeptide with a predicted molecular mass of about 28.7 kDa. The deduced amino acid sequence comparison and phylogenetic analysis indicated that Spi1C and some partial proteinase inhibitor I4 serpins were closely related. Functional characterization demonstrated that the recombinant Spi1C protein could inhibit a series of serine proteases. The Spi1C protein exhibited inhibitory activity against alpha-chymotrypsin and trypsin with K-i values of around 1.79 x 10(-8) and 1.52 x 10(-8) M, respectively. No inhibition activity was exhibited against elastase. Using H-D-Phe-Pip-Arg-pNA as the chromogenic substrate, the optimum pH and temperature of the inhibition activity against trypsin were 7.0-8.0 and 25 degrees C, respectively. The identification of a novel serpin gene underscores the potential of marine metagenome screening for novel biomolecules.