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J. Bacteriol., 01 1997, 430-438, Vol 179, No. 2
M Suzuki, S Taguchi, S Yamada, S Kojima, KI Miura and H Momose
We previously isolated three extracellular endogenous enzymes from a
Streptomyces albogriseolus mutant strain which were targets of Streptomyces
subtilisin inhibitor (SSI) (S. Taguchi, A. Odaka, Y. Watanabe, and H.
Momose, Appl. Environ. Microbiol. 61:180-186, 1995). In the present study,
of the three enzymes the largest one, with a molecular mass of 45 kDa
(estimated by sodium dodecyl sulfate- polyacrylamide gel electrophoresis),
termed SAM-P45, has been characterized in detail. The entire gene encoding
SAM-P45 was cloned as an approximately 10-kb fragment from S. albogriseolus
S-3253 genomic DNA into an Escherichia coli host by using a shuttle plasmid
vector. The amino acid sequence corresponding to the internal region of
SAM- P45, deduced from the nucleotide sequence of the gene, revealed high
homology, particularly in three regions around the active-site residues
(Asp, His, and Ser), with the amino acid sequences of the mature domain of
subtilisin-like serine proteases. In order to investigate the enzymatic
properties of this protease, recombinant SAM-P45 was overproduced in
Streptomyces coelicolor by using a strong SSI gene promoter. Sequence
analysis of the SAM-P45 gene and peptide mapping of the purified SAM-P45
suggested that it is synthesized as a large precursor protein containing a
large C-terminal prodomain (494 residues) in addition to an N-terminal
preprodomain (23 and 172 residues). A high proportion of basic amino acids
in the C-terminal prodomain was considered to serve an element interactive
with the phospholipid bilayer existing in the C-terminal prodomain, as
found in other membrane-anchoring proteases of gram-positive bacteria. It
is noteworthy that SAM-P45 was found to prefer basic amino acids to
aromatic or aliphatic amino acids in contrast to subtilisin BPN', which has
a broad substrate specificity. The hydrolysis by SAM-P45 of the synthetic
substrate (N-succinyl-L-Gly-L-Pro-L-Lys-p-nitroanilide) most preferred by
this enzyme was inhibited by SSI, chymostatin, and EDTA. The proteolytic
activity of SAM-P45 was stimulated by the divalent cations Ca2+ and Mg2+.
From these findings, we conclude that SAM-P45 interacts with SSI and can be
categorized as a novel member of the subtilisin-like serine protease
family.
Copyright © 1997, American Society for Microbiology
A novel member of the subtilisin-like protease family from Streptomyces albogriseolus
Department of Biological Science and Technology, Science University of Tokyo, Noda-shi, Chiba, Japan.
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