Yoshiharu Kimura

Purification and characterization of a protease-resistant cellulase from Aspergillus niger

Abstract An endo-β-1,4-glucanase (EC 3.2.1.4) was purified from a culture filtrate of Aspergillus niger IFO31125 by column chromatography through TSK-gel DEAE-3SW and TSK-gel DEAE-5PW, and by gel filtration through TSK-gel G2000SW by high performance liquid chromatography. The enzyme was estimated to have a molecular weight of about 40 kDa by both gel filtration and SDS-polyacrylamide gel electrophoresis, and appeared to consist of a monomeric protein. It contained 8.9% carbohydrate. The optimal pH for activity was 6.0–7.0, and the stable pH range was 5.0–10.0. The optimum temperature at pH 6.0 was around 70°C. The enzyme was very thermally stable and no loss of original activity was found on incubation at 60°C for 2 h. The enzyme efficiently hydrolyzed carboxymethylcellulose and lichenan, but crystalline forms of cellulose, curdlan, laminarin, cellobiose, p-nitrophenyl-β- d -glucopyranoside and p-nitrophenyl-β- d -cellobioside were barely hydrolyzed. The activity of the enzyme was inhibited by Hg2+ and Cu2+ but was not affected by other inhibitors of thiol enzymes such as p-chloromercuribenzoate and N-ethylmaleimide. N-Bromosuccinimide showed a strong inhibitory effect, suggesting that a tryptophan residue is essential for the activity of the enzyme. The N-terminal amino acid sequence of the enzyme showed considerable homology to those of endo-β-1,4-glucanases from some other microorganisms, including Sclerotinia sclerotiorum and Schizophyllum commune. The enzyme had very strong protease-resistance, and showed no loss of activity when incubated with proteases such as Savinase at 40°C, even for 2 weeks.

Creation of Novel Technologies for Extracellular Protein Production Toward the Development of Bacillus subtilis Genome Factories

Bacillus subtilis has been widely used for the industrial production of useful proteins because of its high protein secretion ability and safety. We focused on genome reduction as a new concept for enhancing production of recombinant enzymes in B. subtilis cells based on detailed analysis of the genome mechanism. First, we reported that a novel B. subtilis strain, MGB874, depleted 20.7 % of the genomic sequence of the wild type by rationally designed deletions to create simplified cells for protein production. When compared with wild-type cells, the productivity of cellulase and protease from transformed plasmids harboring the corresponding genes was markedly enhanced. These results indicate that a bacterial factory specializing in the production of substances can be constructed by deleting the genomic regions unimportant for growth and substance production from B. subtilis. Second, deletion of the rocDEF-rocR region, which is involved in arginine degradation, was found to contribute to the improvement of enzyme production in strain MGB874. The present study indicated that our results demonstrated the effectiveness of a synthetic genomic approach with reduction of genome size to generate novel and useful bacteria for industrial uses. Furthermore, the design of the changes in the transcriptional regulatory network of the nitrogen metabolic pathway in B. subtilis cells could facilitate the generation of improved industrial protein production.