The determination of molecular weights of Streptomyces subtilisin inhibitor and the complex of Streptomyces subtilisin inhibitor and subtilisin BPN' by sedimentation equilibrium

Potential Anticoagulant Activity of Trypsin Inhibitor Purified from an Isolated Marine Bacterium Oceanimonas Sp. BPMS22 and its Kinetics

Protease inhibitors control major biological protease activities to maintain physiological homeostasis. Marine bacteria isolated from oligotrophic conditions could be taxonomically distinct, metabolically unique, and offers a wide variety of biochemicals. In the present investigation, marine sediments were screened for the potential bacteria that can produce trypsin inhibitors. A moderate halotolerant novel marine bacterial strain of Oceanimonas sp. BPMS22 was isolated, identified, and characterized. The effect of various process parameters like salt concentration, temperature, and pH was studied on the growth of the bacteria and production of trypsin inhibitor. Further, the trypsin inhibitor was purified to near homogeneity using anion exchange, size exclusion, and affinity chromatography. The purified trypsin inhibitor was found to competitively inhibit trypsin activity with an inhibition coefficient, K_i, of 3.44 ± 0.13 μM and second-order association rate constant, k_ass, of 1.08 × 10³ M^-1 S^-1. The proteinaceous trypsin inhibitor had a molecular weight of approximately 30 kDa. The purified trypsin inhibitor showed anticoagulant activity on the human blood samples.

A novel double-headed proteinaceous inhibitor for metalloproteinase and serine proteinase

A novel proteinaceous inhibitor for the metalloproteinase of Streptomyces caespitosus has been isolated from the culture supernatant of Streptomyces sp. I-355. It was named ScNPI (Streptomyces caespitosus neutral proteinase inhibitor). ScNPI exhibited strong inhibitory activity toward ScNP with a K(i) value of 1.6 nm. In addition, ScNPI was capable of inhibiting subtilisin BPN' (K(i) = 1.4 nm) (EC ). The scnpi gene consists of two regions, a signal peptide (28 amino acid residues) and a mature region (113 amino acid residues, M(r) = 11,857). The deduced amino acid sequence of scnpi showed high similarity to those of Streptomyces subtilisin inhibitor (SSI) and its homologues. The reactive site of ScNPI for inhibition of subtilisin BPN' was identified to be Met(71)-Tyr(72) bond by specific cleavage. To identify the reactive site for ScNP, Tyr(33) and Tyr(72), which are not conserved among other SSI family inhibitors but are preferable amino acid residues for ScNP, were replaced separately by Ala. The Y33A mutant retained inhibitory activity toward subtilisin BPN' but did not show any inhibitory activity toward ScNP. Moreover, a dimer of ternary complexes among ScNPI, ScNP, and subtilisin BPN' was formed to give the 2:2:2 stoichiometry. These results strongly indicate that ScNPI is a double-headed inhibitor that has individual reactive sites for ScNP and subtilisin BPN'.

Crystal structure at 2.6 A resolution of the complex of subtilisin BPN' with streptomyces subtilisin inhibitor

The crystal structure of the complex of a bacterial alkaline serine proteinase, subtilisin BPN', with its proteinaceous inhibitor SSI (Streptomyces subtilisin inhibitor) was solved at 2.6 A resolution. Compared with other similar complexes involving serine proteinases of the trypsin family, the present structure is unique in several respects. (1) In addition to the usual antiparallel beta-sheet involving the P1, P2 and P3 residues of the inhibitor, the P4, P5 and P6 residues form an antiparallel beta-sheet with a previously unnoticed chain segment (residues 102 through 104, which was named the S4-6 site) of subtilisin BPN'. (2) The S4-6 site does not exist in serine proteinases of the trypsin family, whether of mammalian or microbial origin. (3) Global induced-fit movement seems to occur on SSI: a channel-like structure in SSI where hydrophobic side-chains are sandwiched between two lobes becomes about 2 A wider upon complexing with subtilisin. (4) The complex is most probably a Michaelis complex, as in most of the other complexes. (5) The main role of the "secondary contact region" of SSI seems to be to support the reactive site loop ("primary contact region"). Steric homology of the two contact regions between the inhibitors of the SSI family and the pancreatic secretory trypsin inhibitor-ovomucoid inhibitor family is so high that it seems to indicate divergent evolutionary processes and to support the general notion as to the relationship of prokaryotic and eukaryotic genes put forward by Doolittle (1978).