A subtilisin inhibitor produced by Streptomyces bikiniensis possesses a glutamine residue at reactive site P1.
We determined the complete amino acid sequence of a novel subtilisin inhibitor, SIL15, which had been isolated from the culture supernatant of Streptomyces bikiniensis and shown to be a member of the Streptomyces subtilisin inhibitor (SSI)-like (SIL) protein family, and then identified its reactive site. SIL15 is composed of 113 amino acids and exists as a dimer. Compared with other SSI-family inhibitors, SIL15 was found to be unique in that it possesses a Gln residue at the P1 site of the reactive site and has two-residue insertions in two regions, one in the alpha 1-helix and the other in the flexible loop region near the reactive site. Inhibition of subtilisin BPN' by SIL15 (inhibitor constant, 2.7 x 10(-11) M) was due to the presence of a Gln residue at the P1 site, which was well consistent with the results obtained for P1-site mutants of SSI and turkey ovomucoid domain 3.
Terabe
M
M
Institute for Biomolecular Science, Gakushuin University, Tokyo.
Kojima
S
S
Taguchi
S
S
Momose
H
H
Miura
K
K
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000096:biosynthesis*; D001665:Binding Sites; D005973:Glutamine / Q000737:chemistry*; D008969:Molecular Sequence Data
D001426:Bacterial Proteins; C018150:subtilisin inhibitor protein, Streptomyces; D005973:Glutamine