Substrate specificity of alkaline proteinase from Aspergillus sojae, a soy sauce producing fungus

High-level expression, purification, and enzymatic characterization of a recombinant Aspergillus sojae alkaline protease in Pichia pastoris

An alkaline protease (Ap) was cloned from Aspergillus sojae GIM3.33 via RT-PCR technique. A truncated Ap without the signal peptide was successfully expressed in the Pichia pastoris KM71 strain. The following describes the optimal process conditions for the recombinant engineering of a strain expressing a recombinant Ap (rAp) in a triangular flask: inoculum concentration OD₆₀₀ value 20.0 in 40 mL working volume (in 500 mL flasks), methanol addition (1.0%; volume ratio), 0.02% biotin solution (60 μL), and YNB primary concentration (13.0 g/L). Under these conditions, the protease activity of rAp in the fermentation broth reached 400.4 ± 40.5 U/mL after induction for three days. The rAp was isolated and purified, and its enzymatic characteristics were tested. Its optimal pH was 10.0, and it remained stable in a pH range of 7.0-10.0. Its optimal temperature was 45 °C and it retained >50% activity at 40 °C for 60 min. The rAp activity was significantly inhibited by PMSF, Zn²⁺ and Fe²⁺ and the rAp had a broad substrate specificity for natural proteins and synthetic peptide substrates, and preferred substrates at P1 position with large hydrophobic side-chain groups. Compared to Papain (8.7%) and Alcalase (12.2%), the degree of hydrolysis of rAp to soy protein isolate was 16.5%; therefore, rAp was a good candidate for the processing of food industry byproducts.

Aspzincin, a family of metalloendopeptidases with a new zinc-binding motif. Identification of new zinc-binding sites (His(128), His(132), and Asp(164)) and three catalytically crucial residues (Glu(129), Asp(143), and Tyr(106)) of deuterolysin from Aspergillus oryzae by site-directed mutagenesis

Deuterolysin (EC 3.4.24.39; formerly designated as neutral proteinase II) from Aspergillus oryzae, which contains 1 g atom of zinc/mol of enzyme, is a single chain of 177 amino acid residues, includes three disulfide bonds, and has a molecular mass of 19,018 Da. Active-site determination of the recombinant enzyme expressed in Escherichia coli was performed by site-directed mutagenesis. Substitutions of His(128) and His(132) with Arg, of Glu(129) with Gln or Asp, of Asp(143) with Asn or Glu, of Asp(164) with Asn, and of Tyr(106) with Phe resulted in almost complete loss of the activity of the mutant enzymes. It can be concluded that His(128), His(132), and Asp(164) provide the Zn(2+) ligands of the enzyme according to a (65)Zn binding assay. Based on site-directed mutagenesis experiments, it was demonstrated that the three essential amino acid residues Glu(129), Asp(143), and Tyr(106) are catalytically crucial residues in the enzyme. Glu(129) may be implicated in a central role in the catalytic function. We conclude that deuterolysin is a member of a family of Zn(2+) metalloendopeptidases with a new zinc-binding motif, aspzincin, defined by the "HEXXH + D" motif and an aspartic acid as the third zinc ligand.

A heat-labile serine proteinase from Penicillium citrinum

A serine proteinase from Penicillium citrinum was purified. The M(r) and isoelectric point were determined as about 26,000 and 9.5, respectively. Activity was retained up to above 40 degrees at pH 7 for 30 min, but the enzyme was completely inactivated at 50 degrees. The first amino acids in the N-terminal region were ANVVQSNVPSWGLARISSKRPGTTSYTYDSTAGEGVVFYGVDTG. The specificity differs from that of other serine proteinases. Kinetic studies on fluorogenic substrates were determined.

Specificities of extracellular and ribosomal serine proteinases from Bacillus natto, a food microorganism

The specificities of extracellular and ribosomal serine proteinase from Bacillus natto, a food microorganism, were investigated. Both proteins have highly restricted and characteristic specificities. With the extracellular serine proteinase, initial cleavage site was observed at Leu15-Tyr16, secondary site at Ser9-His10 and additional cleavage sites at Gln4-His5 and His5-Leu6 in the oxidized insulin B-chain. Hydrolysis of proangiotensin with the extracellular serine proteinase was observed primarily at Phe8-His9 and secondary at Tyr4-Ile5. The extracellular serine proteinase has a Km of 0.08 mM and kcat of 3 S-1 for angiotensin hydrolysis. With the ribosomal proteinase, initial cleavage site of the oxidized insulin B-chain was observed at Leu15-Tyr16 and additional cleavage site at Phe24-Phe25. Hydrolysis of proangiotensin was observed at Tyr4-Ile5 bond with the ribosomal proteinase.

Multiple forms of protyrosinase from Aspergillus oryzae and their mode of activation at pH 3.0

This paper describes the isolation of three molecular forms (I-III) of protyrosinase and catalytically active tyrosinase ( monophenol ,dihydroxyphenylalanine: oxygen oxidoreductase, E.C. 1.14.18.1) from fresh mycelia of Aspergillus oryzae BIR 128 by (NH4)2SO4 fractionation, successive chromatographies and disc-gel electrophoresis. Experimental evidence is presented that purified protyrosinase is contaminated with firmly attached proteinases, and that this contamination may account for both the multiple molecular forms of protyrosinase /tyrosinase and the activation of the proenzyme at acidic pH (2.5-3.0). The activation process of protyrosinase seems to be the result of a cleavage of the polypeptide chain by aspartic proteinase from Aspergillus (EC 3.4.23.6) in the purified protyrosinase preparation. Protyrosinase and tyrosinase have different conformation, different stabilities and some different properties.