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A crystallographic study reveals the structural basis for regulation by two different inhibitors of the actin capping protein, a critical factor controlling actin-driven cell motility.

Actin depolymerizing factor (ADF) and cofilin accelerate actin dynamics by severing and disassembling actin filaments. Here, we present the 3.8 Å resolution cryo-EM structure of cofilactin (cofilin-decorated actin filament). The actin subunit structure of cofilactin (C-form) is distinct from those of F-actin (F-form) and monomeric actin (G-form). During the transition between these three conformations, the inner domain of actin (subdomains 3 and 4) and the majority of subdomain 1 move as two separate rigid bodies. The cofilin–actin interface consists of three distinct parts. Based on the rigid body movements of actin and the three cofilin–actin interfaces, we propose models for the cooperative binding of cofilin to actin, preferential binding of cofilin to ADP-bound actin filaments and cofilin-mediated severing of actin filaments.

The intracellular distribution and migration of many protein complexes and organelles is regulated by the dynamics of the actin filament. Many actin filament endbinding proteins play crucial roles in actin dynamics, since polymerization and depolymerization of actin protomers occur only at the filament ends. We present here an EM structure of the complex of the actin filament and hetero-dimeric capping protein (CP) bound to the barbedend at 23 Å resolution, by applying a newly developed methods of image analysis to cryo-electron micrographs. This structure was fitted by the crystal structure of CP and the proposed actin filament structure, allowing us to construct a model that depicts two major binding regions between CP and the barbed-end. This binding scheme accounted for the results of newly performed and previously published mutation experiments, and led us to propose a two-step binding model. This is the first determination of an actin filament end structure.

Glucocorticoid hormones are important in the maintenance of many brain functions. Although their receptors are distributed abundantly throughout the brain, including the prefrontal cortex (PFC), it is not clear how glucocorticoid functions, particularly with regard to cognitive processing in the PFC. There is evidence of PFC cognitive deficits such as working memory impairment in several stressrelated neuropsychiatric disorders, including depression, schizophrenia, and Parkinson's disease. Disruption of the hypothalamopituitary-adrenal (HPA) system, which is characterized by attenuated glucocorticoid negative feedback, is also observed. In rats, chronic stress induces working memory impairment as a result of decreased dopaminergic transmission in the PFC. These chronically stressed rats also show HPA disruption; this is caused in part by a reduced glucocorticoid response in the PFC. These findings implicate reduced glucocorticoid actions in working memory impairment. In the present study, we examined the effects of the suppression of endogenous glucocorticoids by adrenalectomy (ADX) on working memory in rats and explored the involvement of PFC dopaminergic activities in memory. The ADX impaired working memory, decreased dopamine release, and upregulated D 1 receptors in the PFC. These dysfunctions were prevented by corticosterone replacement that reproduced normal physiological plasma levels, indicating that suppression of glucocorticoids causes these dysfunctions. Moreover, the ADX-induced working memory impairment was ameliorated by intra-PFC infusions of a D 1 receptor agonist, SKF 81297. Thus, suppression of glucocorticoids impaired working memory through a D 1 receptormediated hypodopaminergic mechanism in the PFC. This finding indicates that endogenous glucocorticoids are essential for maintaining PFC cognitive function and suggests that HPA disruption contributes to PFC cognitive deficits.

To clarify the metabolic fate of glycyrrhizin when orally ingested, we investigated the bioavailability of glycyrrhetic acid, the aglycone of glycyrrhizin, after intravenous or oral administration of glycyrrhetic acid (5.7 mg kg-1, equimolar to glycyrrhizin) or glycyrrhizin (10 mg kg-1) at a therapeutic dose in rat. Plasma concentration of glycyrrhetic acid rapidly decreased after its intravenous administration, with AUC of 9200 +/- 1050 ng h mL-1 and MRT of 1.1 +/- 0.2 h. The AUC and MRT values after oral administration were 10600 +/- 1090 ng h mL-1 and 9.3 +/- 0.6 h, respectively. After oral administration of glycyrrhizin, the parent compound was not detectable in plasma at any time, but glycyrrhetic acid was detected at a considerable concentration with AUC of 11700 +/- 1580 ng h mL-1 and MRT of 19.9 +/- 1.3 h, while glycyrrhetic acid was not detected in plasma of germ-free rats at 12 h after oral administration of glycyrrhizin. The AUC value of glycyrrhetic acid after oral administration of glycyrrhizin was comparable with those after intravenous and oral administration of glycyrrhetic acid, indicating a complete biotransformation of glycyrrhizin to glycyrrhetic acid by intestinal bacteria and a complete absorption of the resulting glycyrrhetic acid from intestine. Plasma glycyrrhizin rapidly decreased and disappeared in 2 h after intravenous administration. AUC and MRT values were 2410 +/- 125 micrograms min mL-1 and 29.8 +/- 0.5 min, respectively. Plasma concentration of glycyrrhetic acid showed two peaks a small peak at 30 min and a large peak at 11.4 h, after intravenous administration of glycyrrhizin, with an AUC of 15400 +/- 2620 ng h L-1 and an MRT of 18.8 +/- 1.0 h. The plasma concentration profile of the latter large peak was similar to that of glycyrrhetic acid after oral administration of glycyrrhizin, which slowly appeared and declined. The difference of MRT values (19.9 and 9.3 h) for plasma glycyrrhetic acid after oral administration of glycyrrhizin and glycyrrhetic acid suggests the slow conversion of glycyrrhizin into glycyrrhetic acid in the intestine.

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Behavioral and psychological symptoms of dementia (BPSD), including anxiety, depression, excitement, anger, hallucination, and roaming, are seen in patients with Alzheimer's disease and other forms of senile dementia. 1,2) To date, although atypical or conventional antipsychotic medications are used to treat BPSD, drug-induced extrapyramidal symptoms and other adverse events are seen. In addition, the Food and Drug Administration warned in 2005 that the antipsychotic medications increase mortality among elderly patients. Therefore, new remedies without adverse effects have been sought.Yokukansan (TJ-54) is a traditional herbal medicine called a 'kampo medicine' in Japan. The Ministry of Health, Labor and Welfare in Japan has approved it as a remedy for neurosis, insomnia, and irritability in children. Recently, TJ-54 has been reported to ameliorate excitement, anger, and hallucination in BPSD in patients with Alzheimer's disease, dementia with Lewy bodies, and other forms of senile dementia. 1,2) However, there is limited research on this compound and the mechanism by which it alters the symptoms of dementia is unknown.Up to now, various dementia models including b-amyloid protein precursor (APP) 3) or a-synuclein transgenic mice, 4) and ischemia 5) or scopolamine 6) -treated animals have been used for research in the pathogenesis and therapy of dementia. However, because most studies focused on deficits of the functions of learning and memory that are the main symptoms of dementia, or because only the abnormalities of learning and memory functions are observed in the most models, information regarding BPSD was few in the animal models. Thus, animal models covering peripheral symptoms like BPSD observed in patients with dementia have little been reported. However, recently, it has been reported that not only impairment of learning and memory but also BPSD-like behaviors such as anxiety, depression, muricide, attacking, and startle responses are observed in thiamine-deficient (TD) rats and mice, 7) i.e., the data about BPSD-like behaviors are more abundant than other dementia models. TD is a critical factor in the etiology of Wernicke-Korsakoff's syndrome, which is characterized by a decrease in thiamine pyrophosphate (biologically active form of thiamine)-dependent enzymes involved in cellular glucose and energy metabolism in the brain.8) Thus, although the pathogenesis (or an induction factor) in each dementia model including TD animals is different, there is a common point that memory dysfunction is observed in each model. Furthermore, similar deficiencies in thiamine pyrophosphate-dependent enzyme activities are reported in postmortem brain tissues of patients with Alzheimer's disease. 9) TD has been also reported to induce selective neuronal loss, 10) cholinergic deficits, 11) and accumulations of the abnormal tau isoforms 12) and APP 13) that are involved in Alzheimer's disease. These findings suggest that TD animals may be a valuable tool for evaluation of pharmacotherapy for BPSD as well as dysfunction ...