Hirokazu Usuki

Production of dipeptidyl peptidase IV inhibitory peptides from defatted rice bran

The insulinotropic hormone glucagon-like peptide-1 is metabolised extremely rapidly by the ubiquitous enzyme dipeptidyl peptidase IV (DPP-IV). Therefore, human DPP-IV is a key regulator involved in the prevention and treatment of type 2 diabetes. To simplify the method of producing an inhibitory peptide against DPP-IV, we focused on rice bran (RB) as a source and subjected proteins from defatted RB to enzymatic proteolysis using 2 commercial enzymes. The RB peptides produced with Umamizyme G exhibited 10 times the inhibitory activity as those produced with Bioprase SP. The half-maximal inhibitory concentration (IC(50)) value of the RB peptides was 2.3 ± 0.1mg/ml. Leu-Pro and Ile-Pro were identified as the inhibitory peptides among the RB peptides produced with Umamizyme G. Ile-Pro was the strongest DPP-IV inhibitor among the 15 Xaa-Pro dipeptides and Pro-Ile tested. Ile-Pro competitively inhibited DPP-IV (K(i)=0.11 mM). Mass spectrometry indicated that the contents of Leu-Pro and Ile-Pro in the RB peptides were 2.91 ± 0.52 μg/mg.

Pochonicine, a polyhydroxylated pyrrolizidine alkaloid from fungus Pochonia suchlasporia var. suchlasporia TAMA 87 as a potent β-N-acetylglucosaminidase inhibitor

A new polyhydroxylated pyrrolizidine alkaloid designated as pochonicine (1) was isolated from a solid fermentation culture of the fungal strain Pochonia suchlasporia var. suchlasporia TAMA 87. The structure of 1 was determined using NMR and MS techniques as (1R*, 3S*, 5S*, 6S*, 7R*, 7a S*)-5-acetamidomethyl-3-hydroxymethyl-1,6,7-trihydroxypyrrolizidine. Pochonicine (1) showed potent inhibition against beta-N-acetylglucosaminidases (GlcNAcases) of various organisms including insects, fungi, mammals, and a plant but no inhibition against beta-glucosidase of almond, alpha-glucosidase of yeast, or chitinase of Bacillus sp. The GlcNAcase inhibitory activity of pochonicine (1) was comparable to nagstatin, a potent GlcNAcase inhibitor of natural origin.

pTONA5: A hyperexpression vector in streptomycetes

We constructed the Streptomyces hyperexpression vector pTONA5 based on pIJ702 vector; it includes a metalloendopeptidase (SSMP) promoter isolated from Streptomyces cinnamoneus TH-2 and a metalloendopeptidase terminator isolated from Streptomyces aureofaciens TH-3. The vector contains recognition sites for restriction enzymes NdeI and EcoRI/XbaI/HindIII between the promoter and terminator to facilitate heterologous gene cloning. The plasmids were transferred from Escherichia coli to streptomycetes via conjugation from oriT; the transformants were able to be selected using kanamycin and/or thiostrepton. The SSMP promoter functions constitutively in the presence of a rich inorganic phosphate source and glucose. We constructed expression plasmids including three Streptomyces aminopeptidases-leucine aminopeptidase, proline aminopeptidase (PAP), and aminopeptidase P (APP)-using the pTONA5 vector and Streptomyces lividans. Although they lack signal peptides for secretion, PAP and APP were secreted at high levels in the culture broth.

Characterization of calcium ion sensitive region for β-Mannanase from Streptomyces thermolilacinus

Despite the widespread industrial applications of β-mannanase, the relations between the enzymatic properties and metal ions remain poorly understood. To elucidate the effects of metal ions on β-mannanase, thermal stability and hydrolysis activity were characterized. The stman and tfman genes encoding β-mannanase (EC.3.2.1.78) from Streptomyces thermolilacinus NBRC14274 and Thermobifida fusca NBRC14071 were cloned and expressed in Escherichia coli. The thermal stability of each enzyme shifted to the 7-9°C high temperature in the presence of Ca(2+) compared with that in the absence of Ca(2+). These results show that the thermal stability of StMan and TfMan was enhanced by the presence of Ca(2+). StMan, but not TfMan, required Ca(2+) for the hydrolysis activity. To identify the Ca(2+) sensitive region of StMan, we prepared eight chimeric enzymes. Based on the results of the relationship between Ca(2+) and hydrolysis activity, the region of amino-acid residues 244-349 of StMan was responsible for a Ca(2+) sensitive site.

Highly potent fibrinolytic serine protease from Streptomyces.

We introduce a highly potent fibrinolytic serine protease from Streptomyces omiyaensis (SOT), which belongs to the trypsin family. The fibrinolytic activity of SOT was examined using in vitro assays and was compared with those of known fibrinolytic enzymes such as plasmin, tissue-type plasminogen activator (t-PA), urokinase, and nattokinase. Compared to other enzymes, SOT showed remarkably higher hydrolytic activity toward mimic peptides of fibrin and plasminogen. The fibrinolytic activity of SOT is about 18-fold higher than that of plasmin, and is comparable to that of t-PA by fibrin plate assays. Furthermore, SOT had some plasminogen activator-like activity. Results show that SOT and nattokinase have very different fibrinolytic and fibrinogenolytic modes, engendering significant synergetic effects of SOT and nattokinase on fibrinolysis. These results suggest that SOT presents important possibilities for application in the therapy of thrombosis.

Extracellular production and characterization of two streptomyces L-asparaginases.

Abstractl-Asparaginase (ASNase) has proved its use in medical and food industries. Sequence-based screening showed the thermophilic Streptomyces strain Streptomyces thermoluteus subsp. fuscus NBRC 14270 (14270 ASNase) to positive against predicted ASNase primary sequences. The 14270 ASNase gene and four l-asparaginase genes from Streptomyces coelicolor, Streptomyces avermitilis, and Streptomyces griseus (SGR ASNase) were expressed in Streptomyces lividans using a hyperexpression vector: pTONA5a. Among those genes, only 14270 ASNase and SGR ASNase were successful for overexpression and detected in culture supernatants without an artificial signal peptide. Comparison of the two Streptomyces enzymes described above demonstrated that 14270 ASNase was superior to SGR ASNase in terms of optimum temperature, thermal stability, and pH stability.

Two bacterial collagenolytic serine proteases have different topological specificities

From among 2000 soil isolates, we purified a secreted serine protease from Streptomyces omiyaensis (SOT), which has extremely high gelatinolytic activity. Using sequence analysis, the primary structure of SOT showed 77% identity with that of S. griseus trypsin (SGT). We constructed recombinants SOT and SGT using S. lividans. They indicated similar properties on optimum pH and temperature, thermostability, and substrate preference using fluorescence energy transfer combinatorial libraries. SOT greatly hydrolyzed both type I and type IV collagens, but SGT has poor ability to hydrolyze type IV collagen. Furthermore, SOT exhibits higher hydrolytic activities toward other protein substrate such as gelatin and casein than SGT. These results suggest that these two enzymes have different topological specificities in spite of their similar primary structures. We also constructed chimeras between SOT and SGT to investigate which domain is associated with differences in their substrate specificity. In comparison to substrate specificities of chimeras, we found that the N-terminal domain contributes to the determination of topological specificity.

Activation of oligopeptidase B from Streptomyces griseus by thiol-reacting reagents is independent of the single reactive cysteine residue

Oligopeptidase B from Streptomyces griseus was cloned and characterized to clarify the substrate recognition mechanism and the role of a reactive cysteine residue in family S9 prolyl oligopeptidases (POPs). The cloned enzyme, SGR-OpdB, was annotated as a putative family S9 prolyl oligopeptidase based on its deduced amino acid sequence, in which a sole cysteine residue Cys(544) is present close to the catalytic Asp residue in the C-terminal region. The protein was identified as oligopeptidase B, a member of the subfamily S9a of the family S9 POPs, as judged by its substrate specificity and enzymatic characteristics. Its enzymatic activity was markedly enhanced by high NaCl concentration and the reducing reagents dithiothreitol (DTT) and reduced glutathione (GSH). It is particularly interesting that oxidized glutathione (GSSG) also enhanced SGR-OpdB activity. The SGR-OpdB C544A mutant was constructed and characterized to clarify the role of the putative reactive Cys residue, Cys(544). Surprisingly, the enzymatic activity of the Cys-free mutant was also markedly activated by the general thiol-reacting reagent DTT, GSH, and GSSG. To our knowledge, this is the first report of activity-enhancing effects of thiol-reacting reagents toward Cys-free enzymes. Results clarified the role of additives in inducing conformational change of SGR-OpdB into active peptidase.

The Aminolysis Reaction of Streptomyces S9 Aminopeptidase Promotes the Synthesis of Diverse Prolyl Dipeptides

ABSTRACT Prolyl dipeptide synthesis by S9 aminopeptidase from Streptomyces thermocyaneoviolaceus (S9AP-St) has been demonstrated. In the synthesis, S9AP-St preferentially used l-Pro-OBzl as the acyl donor, yielding synthesized dipeptides having an l-Pro-Xaa structure. In addition, S9AP-St showed broad specificity toward the acyl acceptor. Furthermore, S9AP-St produced cyclo (l-Pro-l-His) with a conversion ratio of substrate to cyclo (l-Pro-l-His) higher than 40%.

Peptide bond formation by aminolysin-A catalysis: A simple approach to enzymatic synthesis of diverse short oligopeptides and biologically active puromycins

A new S9 family aminopeptidase derived from the actinobacterial thermophile Acidothermus cellulolyticus was cloned and engineered into a transaminopeptidase by site-directed mutagenesis of catalytic Ser(491) into Cys. The engineered biocatalyst, designated aminolysin-A, can catalyze the formation of peptide bonds to give linear homo-oligopeptides, hetero-dipeptides, and cyclic dipeptides using cost-effective substrates in a one-pot reaction. Aminolysin-A can recognize several C-terminal-modified amino acids, including the l- and d-forms, as acyl donors as well as free amines, including amino acids and puromycin aminonucleoside, as acyl acceptors. The absence of amino acid esters prevents the formation of peptides; therefore, the reaction mechanism involves aminolysis and not a reverse reaction of hydrolysis. The aminolysin system will be a beneficial tool for the preparation of structurally diverse peptide mimetics by a simple approach.