Structural analysis of monomeric isocitrate dehydrogenase from corynebacterium glutamicum

In this research project, structural aspects of monomeric NADP+-dependent isocitrate dehydrogenase from Corynebacterium glutamicum (CgIDH) are investigated together with site-directed mutagenesis and fluorescence spectroscopy studies. CgIDH, one of the enzymes of the Krebs cycle, catalyzes the decarboxylation of isocitrate into α-ketoglutarate, which in some bacteria and plants regulates the flow of carbon into either the Krebs cycle or the glyoxylate bypass depending on the available carbon source. The structure of CgIDH complexed with Mg2+ has been determined at 1.75 Å resolution using X-ray crystallography. In contrast to the closed conformation of published structures of monomeric NADP+-dependent IDH from Azotobactor vinelandii complexed with either isocitrate-Mn2+ or NADP+, the structure of CgIDH complexed with Mg2+ demonstrates the open conformation. The superimposed structure of CgIDH complexed with Mg2+ onto the structures of AvIDH complexes reveals that Domain II is rotated ~24° or ~35º, respectively, relative to Domain I when isocitrate-Mn2+ or NADP+ is bound, resulting in the closure of the active site between the two domains. Fluorescence spectroscopic studies support the proposal that the presence of isocitrate or NADP+ could mediate the conformational changes in CgIDH. In addition, three CgIDH mutants (S130D, K253Q, and Y416T) were created based on the structural analysis and previous mutagenesis studies of homodimeric NADP+-dependent IDH. Both the specific activities and the fluorescence spectra of these CgIDH mutants elucidate the roles of these active site residues in CgIDH catalysis. It has been suggested that the conformational changes observed in the presence of the substrate(s) may regulate enzymatic activity in CgIDH, in contrast to homodimeric NADP+-dependent IDH in Escherichia coli, where the phosphorylation cycle controls activity. It is also presumed that both Lys253 and Tyr416 may play critical roles in CgIDH activity, as do the equivalent residues in homodimeric IDH from porcine heart mitochondria. Similar structural features and conformational changes among monomeric CgIDH and homodimeric NADP+-dependent IDH enzymes suggest the phylogenetic relationships among various monomeric and homodimeric NADP+-dependent IDH from different sources

Chironomid fauna Piptera: Chironomidae) in the Hosomidani valley, western Chugoku Mountains, Japan

The Hosomidani riparian fbrest, located around the origin of the Ohta River basin, is one of the most nature-rich districts in Japan. We investigated chironomid fauna in the Hosomidani valley as　anindicator taxon to evaluate the species diversity of　&eshwater benthic macroinvertebrates. On 23 August and 2 November, 2005, ironomid lalvae were collected in the main stream of the Hosomidani River, small streamletsflowing Into the main stream and the floodplain marsh along the Hosomidani River,and were reared to adults in the laboratory to identify species. A total of 52 species was collected and of which 17 Were newly recorded in the Ohta River basin Thirty-five species were collected in the main stream and of which 14 were also fblmd in the streamiets. On the other hand, 12 out of 16 species collected inthefloodplain marshes were not found in the main streamand streamiets, Polypedilum (Trliodura) caudocula was only found in the noodplain and this is the second record next tothe descnptlOn Of this species in 1991 ･ These results indicate thaHhe high species diversity of cbironomids in tile Hosomidani valley is supported by the presence of the noodplain,Article信州大学山地水環境教育研究センター研究報告 6: 103-108(2010)departmental bulletin pape