The FTDP-17-linked mutation R406W abolishes the interaction of phosphorylated tau with microtubules

The recent finding that several point mutations in the gene encoding for the microtubule-binding protein tau correlate with neurological disorders has heightened interest in the mechanisms of destabilization of this protein. In this study the functional consequences of the tau mutation R406W on the interaction of the protein with microtubules have been analyzed. Mutated tau is less phosphorylated than its normal counterpart at serines 396 and 404. Furthermore, the phosphorylated mutant protein is unable to bind to microtubules, and, as a consequence, microtubules assembled after transient nocodazole treatment in the presence of this tau variant contain only unmodified tau and appear to form more and longer bundles than those assembled in the presence of wild-type tau. We propose that phosphorylated tau, unbound to microtubules, could accumulate in the cytoplasm.     

Semiparametric maximum likelihood for measurement error model regression

This paper presents an EM algorithm for semiparametric likelihood analysis of linear, generalized linear, and nonlinear regression models with measurement errors in explanatory variables. A structural model is used in which probability distributions are specified for (a) the response and (b) the measurement error. A distribution is also assumed for the true explanatory variable but is left unspecified and is estimated by nonparametric maximum likelihood. For various types of extra information about the measurement error distribution, the proposed algorithm makes use of available routines that would be appropriate for likelihood analysis of (a) and (b) if the true x were available. Simulations suggest that the semiparametric maximum likelihood estimator retains a high degree of efficiency relative to the structural maximum likelihood estimator based on correct distributional assumptions and can outperform maximum likelihood based on an incorrect distributional assumption. The approach is illustrated on three examples with a variety of structures and types of extra information about the measurement error distribution.     

Abnormal tau-containing filaments in neurodegenerative diseases

It has been known for some time that the neurofibrillary pathology in Alzheimer's disease consists of so-called paired helical and straight filaments made up of the microtubule-associated protein tau. The degree of dementia observed in the disease correlates better with the extent of neurofibrillary pathology than with the Abeta amyloid deposits, the other characteristic defining pathological fibrous deposit in Alzheimer's disease. However, no familial cases of Alzheimer's disease have been genetically linked to the tau protein locus. Recently a group of frontotemporal dementias with parkinsonism linked to chromosome 17 has been shown to be caused by mutations in the tau gene. Some are missense mutations giving altered tau proteins, whereas others affect the splicing of the pre-mRNA and change the balance between different tau isoforms. Histologically these diseases are all characterised by various kinds of filamentous tau protein deposits, mostly in the complete absence of Abeta deposits. The abnormal tau filaments show different morphologies, depending on the nature of the tau mutation. These diseases show that tau mutations can be a prime cause of inherited dementing illness and may throw some light on the pathological process in the much larger number of sporadic cases of Alzheimer's disease.     

Fibers of tau fragments, but not full length tau, exhibit a cross beta-structure: implications for the formation of paired helical filaments

We have used X-ray fiber diffraction to probe the structure of fibers of tau and tau fragments. Fibers of fragments from the microtubule binding domain had a cross beta-structure that closely resembles that reported both for neurofibrillary tangles found in Alzheimer's disease brain and for fibrous lesions from other protein folding diseases. In contrast, fibers of full-length tau had a different, more complex structure. Despite major differences at the molecular level, all fiber types exhibited very similar morphology by electron microscopy. These results have a number of implications for understanding the etiology of Alzheimer's and other tauopathic diseases. The morphology of the peptide fibers suggests that the region in tau corresponding to the peptides plays a critical role in the nucleation of fiber assembly. The dramatically different structure of the full length tau fibers suggests that some region in tau has enough inherent structure to interfere with the formation of cross beta-fibers. Additionally, the similar appearance by electron microscopy of fibrils with varying molecular structure suggests that different molecular arrangements may exist in other samples of fibers formed from tau.     

糖元合成酶激酶3β对微管相关蛋白tau的磷酸化作用

tau蛋白是中枢神经系统中重要的微管相关蛋白,其功能受磷酸化调节.异常过度磷酸化的tau蛋白是阿尔茨海默病患者脑中神经纤维缠结的主要组成部分.糖元合成酶激酶3β(glycogen synthase kinase-3β,GSK-3β)是重要的tau蛋白激酶之一,它虽可催化tau蛋白多个位点的磷酸化,但对不同位点,其催化效率不同.通过位点特异性、磷酸化依赖的tau蛋白抗体,用免疫印迹技术,检测GSK-3β对tau蛋白位点特异性的磷酸化作用及动力学.用双倒数作图,计算GSK-3β催化tau磷酸化以及各个位点磷酸化的Km值,并结合培养细胞中的实验,研究GSK-3β对tau蛋白磷酸化作用的位点特异性.结果显示,GSK-3β催化tau蛋白多个位点的磷酸化,其中包括Thr181、Ser199、Ser202、Thr205、Thr212、Thr217、Thr231、Ser396和Ser404,对不同的位点磷酸化作用,其Km值不同,GSK-3β对Ser396的Km值最低,即对Ser396位点的亲和性最高,催化其磷酸化的能力最强.在培养的细胞中,也显示了GSK-3β的表达引起Ser396位点的磷酸化最明显.     

The allosteric modulation of thyroxine-binding globulin affinity is entropy driven

Background

Thyroxine-binding globulin (TBG) is a non-inhibitory member of the serpin family of proteins whose main structural element is the reactive center loop (RCL), that, upon cleavage by proteases, is inserted into the protein core adopting a β-strand conformation (stressed to relaxed transition, S-to-R). After S-to-R transition thyroxine (T4) affinity decreases. However, crystallographic studies in the presence or absence of the hormone in different states are unable to show significant differences in the structure and interactions of the binding site. Experimental results also suggest the existence of several S states (differing in the number of inserted RCL residues), associated with a differential affinity.

Methods

To shed light into the molecular basis that regulates T4 affinity according to the degree of RCL insertion in TBG, we performed extended molecular dynamics simulations combined with several thermodynamic analysis of the T4 binding to TBG in three different S states, and in the R state.

Results

Our results show that, despite T4 binding in the protein by similar interactions in all states, a good correlation between the degree of RCL insertion and the binding affinity, driven by a change in TBG conformational entropy, was observed.

Conclusion

TBG allosteric regulation is entropy driven. The presence of multiple S states may allow more efficient T4 release due to protease activity.

General significance

The presented results are clear examples of how computer simulation methods can reveal the thermodynamic basis of allosteric effects, and provide a general framework for understanding serpin allosteric affinity regulation.     

Systemic vaccination with anti‐oligomeric monoclonal antibodies improves cognitive function by reducing Aβ deposition and tau pathology in 3xTg‐AD mice

Alzheimer's disease (AD) is a devastating disorder that is clinically characterized by a comprehensive cognitive decline. Accumulation of the amyloid‐beta (Aβ) peptide plays a pivotal role in the pathogenesis of AD. In AD, the conversion of Aβ from a physiological soluble monomeric form into insoluble fibrillar conformation is an important event. The most toxic form of Aβ is oligomers, which is the intermediate step during the conversion of monomeric form to fibrillar form. There are at least two types of oligomers: oligomers that are immunologically related to fibrils and those that are not. In transgenic AD animal models, both active and passive anti‐Aβ immunotherapies improve cognitive function and clear the parenchymal accumulation of amyloid plaques in the brain. In this report we studied effect of immunotherapy of two sequence‐independent non‐fibrillar oligomer specific monoclonal antibodies on the cognitive function, amyloid load and tau pathology in 3xTg‐AD mice. Anti‐oligomeric monoclonal antibodies significantly reduce the amyloid load and improve the cognition. The clearance of amyloid load was significantly correlated with reduced tau hyperphosphorylation and improvement in cognition. These results demonstrate that systemic immunotherapy using oligomer‐specific monoclonal antibodies effectively attenuates behavioral and pathological impairments in 3xTg‐AD mice. These findings demonstrate the potential of using oligomer specific monoclonal antibodies as a therapeutic approach to prevent and treat Alzheimer's disease.     

AZD1080, a novel GSK3 inhibitor,rescues synaptic plasticity deficits in rodent brain and exhibits peripheral target engagement in humans

Abnormal tau phosphorylation resulting in detachment of tau from microtubules and aggregation are critical events in neuronal dysfunction, degeneration, and neurofibrillary pathology seen in Alzheimer's disease. Glycogen synthase kinase‐3β (GSK3β) is a key target for drug discovery in the treatment of Alzheimer's disease and related tauopathies because of its potential to abnormally phosphorylate proteins and contribute to synaptic degeneration. We report the discovery of AZD1080, a potent and selective GSK3 inhibitor that demonstrates peripheral target engagement in Phase 1 clinical studies. AZD1080 inhibits tau phosphorylation in cells expressing human tau and in intact rat brain. Interestingly, subchronic but not acute administration with AZD1080 reverses MK‐801‐induced deficits, measured by long‐term potentiation in hippocampal slices and in a cognitive test in mice, suggesting that reversal of synaptic plasticity deficits in dysfunctional systems requires longer term modifications of proteins downstream of GSK3β signaling. The inhibitory pattern on tau phosphorylation reveals a prolonged pharmacodynamic effect predicting less frequent dosing in humans. Consistent with the preclinical data, in multiple ascending dose studies in healthy volunteers, a prolonged suppression of glycogen synthase activity was observed in blood mononuclear cells providing evidence of peripheral target engagement with a selective GSK3 inhibitor in humans.     

Optimizing ecosystem function by manipulating pasture community composition

The ability to design plant communities to optimize particular ecosystem functions and thus more effectively provide ecosystem services would improve all types of ecosystem management, including agriculture. We propose a novel quantitative multi-step method for selecting mixtures of plant species to meet ecosystem objectives: collecting trait data; identifying suites of traits related to relevant community processes; relating those processes to the ecosystem functions of interest; optimizing the planted mixture; and evaluating trade-offs. This approach was tested using planted mixtures of 14 grassland species common in managed pastures of the northeastern United States. Ordination of trait data from greenhouse and small plot studies was used to relate species traits to community processes, followed by generalized additive modeling to relate community-weighted mean process scores to field estimates of biomass production and resistance to invasion. Multi-criteria optimization identified seed mixtures that maximized or minimized selected ecosystem functions, facilitating quantification of trade-offs in processual ability within species and between ecosystem functions at the community level. In this study, predicted seasonal and annual biomass values were within expected ranges, but the optimal mixtures differed from forage mixtures traditionally planted in the northeastern United States. Perennial ryegrass was the most commonly-selected grass. Legumes were represented less than expected, possibly due to attributes such as longevity and forage quality that are important in pastures but were not directly included in the optimization. Ecosystem function was not linearly related to species richness. While further research on quantitatively relating species traits and community processes is needed, multi-criteria optimization offers a new path for linking ecosystem function to ecosystem management.