Current Topics in Molecular Biotechnology of a Koji Mold, Aspergillus oryzae(Recent Topics of the Agricultunal Biological Science in Tohoku University)

Aspergillus oryzae is an important filamentous fungus in Japanese fermentation industries and produces a large amount of starch-degrading enzymes, whose gene expressions are regulated by a transcription activator AmyR. We have recently found a gene cluster highly homologous to the yeast maltose-utilizing cluster and showed that expression of the cluster genes is independent on AmyR but is involved in assimilating maltose, a product by starch degradation. In this article are described structural features and expression profiles of the maltose-utilizing cluster genes in A. oryzae. On the other hand, A. oryzae has been expected as a favorable host microorganism for heterologous protein production. In order to understand the bottlenecks for hyperproduction of heterologous proteins in A. oryzae, we have investigated the cellular responses using the mutated α-mannosidase of Aspergillus saitoi as a model protein. Interestingly, the mutated α-mannosidase was secreted as a hyperglycosylated form when overexpressed

Analysis of Expressed Sequence Tags from the Fungus Aspergillus oryzae Cultured Under Different Conditions

We performed random sequencing of cDNAs from nine biologically or industrially important cultures of the industrially valuable fungus Aspergillus oryzae to obtain expressed sequence tags (ESTs). Consequently, 21 446 raw ESTs were accumulated and subsequently assembled to 7589 non-redundant consensus sequences (contigs). Among all contigs, 5491 (72.4%) were derived from only a particular culture. These included 4735 (62.4%) singletons, i.e. lone ESTs overlapping with no others. These data showed that consideration of culture grown under various conditions as cDNA sources enabled efficient collection of ESTs. BLAST searches against the public databases showed that 2953 (38.9%) of the EST contigs showed significant similarities to deposited sequences with known functions, 793 (10.5%) were similar to hypothetical proteins, and the remaining 3843 (50.6%) showed no significant similarity to sequences in the databases. Culture-specific contigs were extracted on the basis of the EST frequency normalized by the total number for each culture condition. In addition, contig sequences were compared with sequence sets in eukaryotic orthologous groups (KOGs), and classified into the KOG functional categories

Biosynthetic assembly of cytochalasin backbone

Cytochalasins are an important class of fungal natural products in view of structural diversity and biological activities. Although their biosynthetic studies have been examined extensively, the detailed molecular assembly mechanism remains to be solved. We have succeeded to heterologously express the cytochalasin polyketide synthase-non-ribosomal peptide synthetase (PKS-NRPS) hybrid gene ccsA and the trans-acting enoyl-CoA reductase gene ccsC in Aspergillus oryzae. The resultant transformant produced a novel metabolite possessing the cytochalasin backbone. This established that CcsA is capable of constructing the octaketide connected with phenylalanine in collaboration with CcsC, and that CcsA R domain catalyzes reductive cleavage of the thio-tethered PKS-NRPS product. (C) 2013 Elsevier Ltd. All rights reserved

Reconstitution of biosynthetic machinery of fungal polyketides : unexpected oxidations of biosynthetic intermediates by expression host

Reconstitution of whole biosynthetic genes in Aspergillus oryzae has successfully applied for total biosynthesis of various fungal natural products. Heterologous production of fungal metabolites sometimes suffers unexpected side reactions by host enzymes. In the studies on fungal polyketides solanapyrone and cytochalasin, unexpected oxidations of terminal olefin of biosynthetic intermediates were found to give one and four by-products by host enzymes of the transformants harboring biosynthetic genes. In this paper, we reported structure determination of by-products and described a simple solution to avoid the undesired reaction by introducing the downstream gene in the heterologous production of solanapyrone C

Biosynthetic Machinery of Diterpene Pleuromutilin Isolated from Basidiomycete Fungi

The diterpene pleuromutilin is a ribosome-targeting antibiotic isolated from basidiomycete fungi, such as Clitopilus pseudo-pinsitus. The functional characterization of all biosynthetic enzymes involved in pleuromutilin biosynthesis is reported and a biosynthetic pathway proposed. In vitro enzymatic reactions and mutational analysis revealed that a labdane-related diterpene synthase, Ple3, catalyzed two rounds of cyclization from geranylgeranyl diphosphate to premutilin possessing a characteristic 5-6-8-tricyclic carbon skeleton. Biotransformation experiments utilizing Aspergillus oryzae transformants possessing modification enzyme genes allowed the biosynthetic pathway from premutilin to pleuromutilin to be proposed. The present study sets the stage for the enzymatic synthesis of natural products isolated from basidiomycete fungi, which are a prolific source of structurally diverse and biologically active terpenoids