Identification of the sprU Gene Encoding an Additional sprT Homologous Trypsin-Type Protease in Streptomyces griseus

Cloning of a 6.6-kb BamHI digested chromosomal DNA from S. griseus IFO13350 revealed the presence of an additional gene encoding a novel trypsin-like enzyme, named SprU. The SprU protein shows a high homology ($79\%$ identity, $88\%$ similarity) with the SGT protease, which has been reported as a bacterial trypsin in the same strain. The amino acid sequence deduced from the nucleotide sequence of the sprU gene suggests that SprU is produced as a precursor consisting of an amino-terminal presequence (29 amino acid residues), prosequence (4 residues), and mature trypsin consisting of 222 amino acids with a molecular weight of 22.94 kDa and a calculated pI of 4.13. The serine, histidine, and aspartic acid residues composing the catalytic triad of typical serine proteases are also well conserved. When the trypsin activity of the SprU was spectrophotometrically measured by the enzymatic hydrolysis of the artificial chromogenic substrate, N-${alpha}$-benzoyl-DL-arginine-p-nitroanilide, the S. lividans transformant with pWHM3-U gave 3 times higher activity than that of control. When the same recombinant plasmid was introduced into S. griseus, however, the gene dosage effect was not so significant, as in the cases of other genes encoding serine proteases, such as sprA, sprB, and sprD. Although two trypsins, SprU and SGT, have a high degree of homology, the pI values, the gene dosage effect in S. griseus, and the gene arrangement adjacent to the two genes are very different, suggesting that the biochemical and biological function of the SprU might be quite different from that of the SGT.