Impact of the Hereditary P301L Mutation on the Correlated Conformational Dynamics of Human Tau Protein Revealed by the Paramagnetic Relaxation Enhancement NMR Experiments.

Tau forms intracellular insoluble aggregates as a neuropathological hallmark of Alzheimer's disease. Tau is largely unstructured, which complicates the characterization of the tau aggregation process. Recent studies have demonstrated that tau samples two distinct conformational ensembles, each of which contains the soluble and aggregation-prone states of tau. A shift to populate the aggregation-prone ensemble may promote tau fibrillization. However, the mechanism of this ensemble transition remains elusive. In this study, we explored the conformational dynamics of a tau fragment by using paramagnetic relaxation enhancement (PRE) and interference (PRI) NMR experiments. The PRE correlation map showed that tau is composed of segments consisting of residues in correlated motions. Intriguingly, residues forming the ß-structures in the heparin-induced tau filament coincide with residues in these segments, suggesting that each segment behaves as a structural unit in fibrillization. PRI data demonstrated that the P301L mutation exclusively alters the transiently formed tau structures by changing the short- and long-range correlated motions among residues. The transient conformations of P301L tau expose the amyloid motif PHF6 to promote tau self-aggregation. We propose the correlated motions among residues within tau determine the population sizes of the conformational ensembles, and perturbing the correlated motions populates the aggregation-prone form.

Catalytic Dearomative Spirocyclization via Gold Carbene Species Derived from Ynamides: Efficient Synthesis of 2-Azaspiro[4.5]decan-3-ones.

An intramolecular catalytic dearomatization of phenols via gold carbene species proceeded to provide 2-azaspiro[4.5]decan-3-ones. The use of NHC ligand and water as a co-solvent was critical for achieving high reactivity. This reaction did not require hazardous diazo compounds as carbene sources and proceeded even under air. The obtained spirocyclic product could be readily transformed into a gabapentin derivative by hydrogenation and deprotection.

Dynamic Allostery Modulates Catalytic Activity by Modifying the Hydrogen Bonding Network in the Catalytic Site of Human Pin1.

Allosteric communication among domains in modular proteins consisting of flexibly linked domains with complimentary roles remains poorly understood. To understand how complementary domains communicate, we have studied human Pin1, a representative modular protein with two domains mutually tethered by a flexible linker: a WW domain for substrate recognition and a peptidyl-prolyl isomerase (PPIase) domain. Previous studies of Pin1 showed that physical contact between the domains causes dynamic allostery by reducing conformation dynamics in the catalytic domain, which compensates for the entropy costs of substrate binding to the catalytic site and thus increases catalytic activity. In this study, the S138A mutant PPIase domain, a mutation that mimics the structural impact of the interdomain contact, was demonstrated to display dynamic allostery by rigidification of the α2-α3 loop that harbors the key catalytic residue C113. The reduced dynamics of the α2-α3 loop stabilizes the C113-H59 hydrogen bond in the hydrogen-bonding network of the catalytic site. The stabilized hydrogen bond between C113 and H59 retards initiation of isomerization, which explains the reduced isomerization rate by ~20% caused by the S138A mutation. These results provide new insight into the interdomain allosteric communication of Pin1.

Allosteric Breakage of the Hydrogen Bond within the Dual-Histidine Motif in the Active Site of Human Pin1 PPIase.

Intimate cooperativity among active site residues in enzymes is a key factor for regulating elaborate reactions that would otherwise not occur readily. Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1) is the phosphorylation-dependent cis-trans peptidyl-prolyl isomerase (PPIase) that specifically targets phosphorylated Ser/Thr-Pro motifs. Residues C113, H59, H157, and T152 form a hydrogen bond network in the active site, as in the noted connection. Theoretical studies have shown that protonation to thiolate C113 leads to rearrangement of this hydrogen bond network, with switching of the tautomeric states of adjacent histidines (H59 and H157) [Barman, A., and Hamelberg, D. (2014) Biochemistry 53, 3839-3850]. This is called the "dual-histidine motif". Here, C113A and C113S Pin1 mutants were found to alter the protonation states of H59 according to the respective residue type replaced at C113, and the mutations resulted in disruption of the hydrogen bond within the dual-histidine motif. In the C113A mutant, H59 was observed to be in exchange between ε- and δ-tautomers, which widened the entrance of the active site cavity, as seen by an increase in the distance between residues A113 and S154. The C113S mutant caused H59 to exchange between the ε-tautomer and imidazolium while not changing the active site structure. Moreover, the imidazole ring orientations of H59 and H157 were changed in the C113S mutant. These results demonstrated that a mutation at C113 modulates the hydrogen bond network dynamics. Thus, C113 acts as a pivot to drive the concerted function among the residues in the hydrogen bond network, as theoretically predicted.

[A case of delayed colonic perforation after metallic stent placement for advanced descending colon cancer during bevacizumab-based chemotherapy].

A 73-year-old man with advanced descending colon cancer and peritoneal metastases underwent a self-expandable metallic stent placement under fluoroscopic guidance on October 2007. The stent placement was successful without early complication. After 6 courses of FOLFOX4 followed by 7 courses of FOLFIRI, he received Bevacizumab-based chemotherapy from August 2008. In April 2009, he was admitted to our hospital with severe abdominal pain due to perforation of descending colon. Although emergent surgery was performed, he developed DIC and died on the 21 postoperative days. This case suggests that metallic stent placement for colorectal cancer cases might increase the risk of bowel perforation during Bevacizumab-based chemotherapy.

Hepta-Histidine Inhibits Tau Aggregation.

Tau aggregation is a central hallmark of tauopathies such as frontotemporal lobar degeneration and progressive supranuclear palsy as well as of Alzheimer's disease, and it has been a target for therapeutic development. Herein, we unexpectedly found that hepta-histidine (7H), an inhibitor of the interaction between Ku70 and Huntingtin proteins, suppresses aggregation of Tau-R3 peptides in vitro. Addition of the trans-activator of transcription (TAT) sequence (YGRKKRRQRRR) derived from the TAT protein to 7H increased its permeability into cells, and TAT-7H treatment of iPS cell-derived neurons carrying Tau or APP mutations suppressed Tau phosphorylation. These results indicate that 7H is a promising lead compound for developing anti-aggregation drugs against Tau-related neurodegenerative diseases including Alzheimer's disease (AD).

Modelling and observations of electron beam charging of an insulator/metal bilayer and its impact on secondary electron images in defect inspection equipment.

A self-consistent simulation of secondary electron (SE) emission and charging of a SiO(2) layer with the thickness of several tens of nanometres on Si is incorporated into a trajectory simulation of emitted SEs above the surface, the centre area of which is charged by electron beams (EBs) at the energy range from 300 to 2000 eV. In order to study the influence of the charging of an insulating layer on defect inspection, a pseudo-image is reconstructed from net SE yields calculated at each point of the SiO(2) surface locally applied the positive voltage. The image contrast between charged and uncharged areas is compared with the observation of thermally oxidized layer with the thickness of 24-106 nm on a Si wafer. The image contrast is very sensitive to the thickness of the SiO(2) layer, which is verified by both observed and calculated images. The calculated changes of the images with the layer thickness and the primary electron energy reproduce the experimental observations fairly well. This confirms a highly sensitive detection mechanism for tiny defects in insulating patterns on a metal hard mask for an EB defect inspection equipment.

The trans isomer of Tau peptide is prone to aggregate, and the WW domain of Pin1 drastically decreases its aggregation.

In Alzheimer's, the disease-related protein Tau is hyperphosphorylated and aggregates into neurofibrillary tangles (NFT). The cis isomer of the phosphorylated Thr231-Pro232 has been proposed as a precursor of aggregation ('Cistauosis'), but this aggregation scheme is not yet completely accepted. Here, we synthesized peptides comprising a phosphorylated region including Thr231-Pro232 and an aggregation-core region R1 to investigate isomer-specific-aggregation of Tau. The phosphorylated peptide formed amyloid-like aggregation. This aggregation was observed even in the presence of the catalytic domain of the peptidyl-prolyl-isomerase Pin1, which preferentially converts the cis isomer to the trans isomer, but decreased drastically in the presence of the WW domain of Pin1 selectively binding to the trans isomer. These results indicate that the trans isomer is aggregation-prone and that the WW domain of Pin1 effectively inhibits its aggregation.

Outcome of surgical treatment of hilar cholangiocarcinoma: a special reference to postoperative morbidity and mortality.

BACKGROUND/PURPOSE: Radical resection for hilar cholangiocarcinoma is still associated with significant morbidity and mortality. The aim of this study was to analyze short-term surgical outcomes and to validate our strategies, including preoperative management and selection of operative procedure. METHODS: We surgically treated 146 consecutive patients with hilar cholangiocarcinoma with a management strategy consisting of preoperative biliary drainage, portal vein embolization, and selection of operative procedure based on tumor extension and hepatic reserve. Major hepatectomy was conducted in 126 patients, and caudate lobectomy or hilar bile duct resection in 20 patients. RESULTS: The overall 5-year survival rate was 35.5%, with overall in-hospital mortality and morbidity rates of 3.4 and 44%, respectively. Hyperbilirubinemia (total bilirubin >5 mg/dL, persisted for >7 postoperative days) and liver abscess were the most frequent complications. Five among 9 patients with liver failure (total bilirubin >10 mg/dL) encountered in-hospital mortality. Four out of 5 mortality patients had suffered circulatory impairment of the remnant liver due to other complications. Multivariate analysis revealed that operative time is a single independent significant predictive factor (odds ratio, 1.005; 95% confidence interval, 1.000-1.010, P = 0.04) for postoperative complications. CONCLUSIONS: Aggressive resection for hilar cholangiocarcinoma, performed in accordance with strict management strategy, achieved acceptably low mortality. Prolonged operative time was a risk for morbidity following hepatobiliary resection.

Large-cell neuroendocrine carcinoma in the thymus.

Large-cell neuroendocrine carcinoma in the thymus is a rare cancer that is more aggressive and leads to a poorer prognosis than other thymic epithelial tumors. A 67-year-old woman presented with an anterior mediastinal mass in the thymus. Histological examination after thymectomy revealed large-cell neuroendocrine carcinoma in the thymus. Although the patient received postoperative chemotherapy and radiotherapy, a distant relapse was detected 6 months after the surgery. We reviewed nine cases of this rare cancer that have been reported in Japan. There is no evidence of to support postoperative therapy for large-cell neuroendocrine carcinoma in the thymus. However, it is essential to accumulate and study these cases to understand this disease and prolong patient survival.

The upstream regulator, Rsr1p, and downstream effectors, Gic1p and Gic2p, of the Cdc42p small GTPase coordinately regulate initiation of budding in Saccharomyces cerevisiae.

BACKGROUND: Cdc42p, a Rho family small GTPase, is essential for budding initiation in the yeast Saccharomyces cerevisiae. The homologous proteins Gic1p and Gic2p (Gic1/2p) are effectors of Cdc42p, but their precise functions remain unknown. Rsr1p/Bud1p is a Ras family small GTPase that controls the selection of the budding site. Previous observations suggested that Rsr1p-GTP recruits Cdc24p, a GDP/GTP exchange factor for Cdc42p, at the incipient bud site. However, this model only addresses how Rsr1p determines the budding site, because the rsr1 mutant normally initiates budding. RESULTS: Here we show that a rsr1 gic1 gic2 mutant fails to initiate budding, resulting in unbudded, large, and multinucleated cells. Expression of a dominant active or dominant negative mutant of RSR1 also inhibited the growth of the gic1 gic2 mutant, suggesting that cycling of Rsr1p between the GTP- and GDP-bound forms is required for budding initiation in the gic1 gic2 mutant. Among the mutations in effectors of CDC42, only the gic1 gic2 mutation demonstrated a synthetic lethal interaction with rsr1. Increased gene dosage of CDC42 suppressed defects in budding initiation of rsr1 gic1 gic2 mutants containing additional mutations in other effectors of CDC42, including BNI1, CLA4 or STE20. The polarized localization of Bni1p-GFP (green fluorescent protein) and Cla4p-GFP was lost after depletion of Gic1p in the rsr1 gic2 mutant. CONCLUSION: We propose that Gic1/2p may stabilize or maintain a complex consisting of Cdc42p-GTP and its effectors at the budding site, which are assembled by the action of the Rsr1p-Cdc24p system.