Ohara K

References (2)

Title : Structural Insights into the Low pH Adaptation of a Unique Carboxylesterase from Ferroplasma: Altering the pH optima of two carboxylesterases - Ohara_2014_J.Biol.Chem_289_24499
Author(s) : Ohara K , Unno H , Oshima Y , Hosoya M , Fujino N , Hirooka K , Takahashi S , Yamashita S , Kusunoki M , Nakayama T
Ref : Journal of Biological Chemistry , 289 :24499 , 2014
Abstract : To investigate the mechanism for low pH adaptation by a carboxylesterase, structural and biochemical analyses of EstFa_R (a recombinant, slightly acidophilic carboxylesterase from Ferroplasma acidiphilum) and SshEstI (an alkaliphilic carboxylesterase from Sulfolobus shibatae DSM5389) were performed. Although a previous proteomics study by another group showed that the enzyme purified from F. acidiphilum contained an iron atom, EstFa_R did not bind to iron as analyzed by inductively coupled plasma MS and isothermal titration calorimetry. The crystal structures of EstFa_R and SshEstI were determined at 1.6- and 1.5-A resolutions, respectively. EstFa_R had a catalytic triad with an extended hydrogen bond network that was not observed in SshEstI. Quadruple mutants of both proteins were created to remove or introduce the extended hydrogen bond network. The mutation on EstFa_R enhanced its catalytic efficiency and gave it an alkaline pH optimum, whereas the mutation on SshEstI resulted in opposite effects (i.e. a decrease in the catalytic efficiency and a downward shift in the optimum pH). Our experimental results suggest that the low pH optimum of EstFa_R activity was a result of the unique extended hydrogen bond network in the catalytic triad and the highly negatively charged surface around the active site. The change in the pH optimum of EstFa_R happened simultaneously with a change in the catalytic efficiency, suggesting that the local flexibility of the active site in EstFa_R could be modified by quadruple mutation. These observations may provide a novel strategy to elucidate the low pH adaptation of serine hydrolases.
ESTHER : Ohara_2014_J.Biol.Chem_289_24499
PubMedSearch : Ohara_2014_J.Biol.Chem_289_24499
PubMedID: 25043762
Gene_locus related to this paper: 9eury-q2pce5 , sulsh-q5nu42

Title : FK960, a potential anti-dementia drug, increases synaptic density in the hippocampal CA3 region of aged rats - Moriguchi_2002_Brain.Res_958_381
Author(s) : Moriguchi A , Nakano K , Yamaguchi I , Sano K , Noda K , Hashimoto M , Ohara K , Matsuoka N , Goto T
Ref : Brain Research , 958 :381 , 2002
Abstract : There is accumulating evidence suggesting that synapse formation in the adult brain is dynamically regulated, and that this regulation plays a role in cognitive function. A decrease in synaptic density is reportedly related to memory deficits in aged animals as well as in Alzheimer's patients. FK960 [N-(4-acetyl-1-piperazinyl)-p-fluorobenzamide monohydrate], a novel anti-dementia drug, has been shown to ameliorate experimental amnesia in rats and monkeys through activation of the somatostatinergic nervous system in the hippocampus. Furthermore, FK960 has been shown to be considerably more effective in a model of spontaneous amnesia in aged rats than cholinesterase inhibitors. In the present electron microscopy study, we demonstrated that the density of axodendritic and axosomatic synapses in the hippocampal CA3 region of aged rats was reduced compared to young rats, and that repeated treatment with FK960 for either 3 or 21 days dose-dependently reversed these deficits in aged rats. This FK960-induced increase in synaptic density was transient and density returned to basal levels at 8 days after the final dose. In contrast, FK960 did not alter synaptic density in the cingulate cortex or hippocampal CA1 region in aged rats, nor the CA3 region of young rats. Collectively, these results suggest that FK960 can selectively and reversibly increase synaptic density in the hippocampal CA3 region of aged rats, and that this activity may play a role in its cognitive-enhancing action.
ESTHER : Moriguchi_2002_Brain.Res_958_381
PubMedSearch : Moriguchi_2002_Brain.Res_958_381
PubMedID: 12470874