Cryo-EM structure of cortical microtubules from human parasite Toxoplasma gondii identifies their microtubule inner proteins

In living cells, microtubules (MTs) play pleiotropic roles, which require very different mechanical properties. Unlike the dynamic MTs found in the cytoplasm of metazoan cells, the specialized cortical MTs from Toxoplasma gondii, a prevalent human pathogen, are extraordinarily stable and resistant to detergent and cold treatments. Using single-particle cryo-EM, we determine their ex vivo structure and identify three proteins (TrxL1, TrxL2 and SPM1) as bona fide microtubule inner proteins (MIPs). These three MIPs form a mesh on the luminal surface and simultaneously stabilize the tubulin lattice in both longitudinal and lateral directions. Consistent with previous observations, deletion of the identified MIPs compromises MT stability and integrity under challenges by chemical treatments. We also visualize a small molecule like density at the Taxol-binding site of β-tubulin. Our results provide the structural basis to understand the stability of cortical MTs and suggest an evolutionarily conserved mechanism of MT stabilization from the inside

Toxoplasma bradyzoites exhibit physiological plasticity of calcium and energy stores controlling motility and egress

Toxoplasma gondii has evolved different developmental stages for disseminating during acute infection (i.e., tachyzoites) and establishing chronic infection (i.e., bradyzoites). Calcium ion (Ca(2+)) signaling tightly regulates the lytic cycle of tachyzoites by controlling microneme secretion and motility to drive egress and cell invasion. However, the roles of Ca(2+) signaling pathways in bradyzoites remain largely unexplored. Here, we show that Ca(2+) responses are highly restricted in bradyzoites and that they fail to egress in response to agonists. Development of dual-reporter parasites revealed dampened Ca(2+) responses and minimal microneme secretion by bradyzoites induced in vitro or harvested from infected mice and tested ex vivo. Ratiometric Ca(2+) imaging demonstrated lower Ca(2+) basal levels, reduced magnitude, and slower Ca(2+) kinetics in bradyzoites compared with tachyzoites stimulated with agonists. Diminished responses in bradyzoites were associated with downregulation of Ca(2+)-ATPases involved in intracellular Ca(2+) storage in the endoplasmic reticulum (ER) and acidocalcisomes. Once liberated from cysts by trypsin digestion, bradyzoites incubated in glucose plus Ca(2+) rapidly restored their intracellular Ca(2+) and ATP stores, leading to enhanced gliding. Collectively, our findings indicate that intracellular bradyzoites exhibit dampened Ca(2+) signaling and lower energy levels that restrict egress, and yet upon release they rapidly respond to changes in the environment to regain motility

Glucose sensor O-GlcNAcylation coordinates with phosphorylation to regulate circadian clock.

Posttranslational modifications play central roles in myriad biological pathways including circadian regulation. We employed a circadian proteomic approach to demonstrate that circadian timing of phosphorylation is a critical factor in regulating complex GSK3β-dependent pathways and identified O-GlcNAc transferase (OGT) as a substrate of GSK3β. Interestingly, OGT activity is regulated by GSK3β; hence, OGT and GSK3β exhibit reciprocal regulation. Modulating O-GlcNAcylation levels alter circadian period length in both mice and Drosophila; conversely, protein O-GlcNAcylation is circadianly regulated. Central clock proteins, Clock and Period, are reversibly modified by O-GlcNAcylation to regulate their transcriptional activities. In addition, O-GlcNAcylation of a region in PER2 known to regulate human sleep phase (S662-S674) competes with phosphorylation of this region, and this interplay is at least partly mediated by glucose levels. Together, these results indicate that O-GlcNAcylation serves as a metabolic sensor for clock regulation and works coordinately with phosphorylation to fine-tune circadian clock

Crystallization and preliminary X-ray diffraction analyses of several forms of the CfaB major subunit of enterotoxigenic Escherichia coli CFA/I fimbriae

Three fusion proteins were generated in order to resolve the atomic structure of the CFA/I fimbriae of enterotoxigenic E. coli. CfaEB is a fusion of the minor and major CFA/I subunits, while CfaBB and CfaBBB are tandem fusions of two and three repeats, respectively, of the major subunit. Each protein was crystallized and the crystal structures of each of these fusions were determined successively by the molecular-replacement method using the CfaE crystal structure as an initial phasing model

Highly sensitive and selective Love mode surface acoustic wave ammonia sensor based on graphene oxides operated at room temperature

It is crucial to develop highly sensitive and selective sensors for ammonia, one of the most common toxic gases which have been widely used in pharmaceutical, chemical and manufacturing industries. In this study, graphene oxide (GO) film was spin-coated onto surfaces of ST-cut quartz surface acoustic wave (SAW) devices with a resonant frequency of 200 MHz for ammonia sensing. The oxygen-containing functional groups (such as hydroxyl and epoxy ones) on the surface of GO film strongly absorb ammonia molecules and thus increase the film stiffness. This is attributed to the main ammonia sensing mechanism of the Love mode SAW devices, which show not only a positive frequency shift of 620 Hz for 500 ppb ammonia gas, but also an excellent selectivity (as compared to other gases such as H2, H2S, CO and NO2) and a good reproducibility, operated at room temperature of 22 oC

A global Carleman estimate in a transmission wave equation and application to a one-measurement inverse problem

We consider a transmission wave equation in two embedded domains in $R^2$, where the speed is $a1 > 0$ in the inner domain and $a2 > 0$ in the outer domain. We prove a global Carleman inequality for this problem under the hypothesis that the inner domain is strictly convex and $a1 > a2$ . As a consequence of this inequality, uniqueness and Lip- schitz stability are obtained for the inverse problem of retrieving a stationary potential for the wave equation with Dirichlet data and discontinuous principal coefficient from a single time-dependent Neumann boundary measurement

Affective Decision-making Predictive of Chinese Adolescent Drinking Behaviors

The goal of the current investigation was to address whether affective decision making would serve as a unique neuropsychological marker to predict drinking behaviors among adolescents. We conducted a longitudinal study of 181 Chinese adolescents in Chengdu city, China. In their 10th grade (ages 15–16), these adolescents were tested for their affective decision-making ability using the Iowa Gambling Task (IGT) and working memory capacity using the Self-Ordered Pointing Test. Self-report questionnaires were used to assess academic performance and drinking behaviors. At 1-year follow-up, questionnaires were completed to assess drinking behaviors, and the UPPS Impulsive Behavior Scale was used to examine four dimensions of impulsivity: urgency, lack of premeditation, lack of perseverance, and sensation seeking. Results indicated that those adolescents who progressed to binge drinking or exhibited consistent binge drinking not only performed poorly on the IGT but also scored significantly higher in urgency compared to those who never or occasionally drank. Moreover, better IGT scores predicted fewer drinking problems and fewer drinks 1 year later after controlling for demographic variables, the previous drinking behaviors, working memory, and impulsivity. These findings suggest that deficits in affective decision making may be important independent determinants of compulsive drinking and potentially addictive behavior in adolescents. (JINS, 2009, 15, 547–557.

Genomic diversity among Basmati rice (Oryza sativa L) mutants obtained through 60Co gamma radiations using AFLP markers

Mutation breeding can be considered successful in obtaining new cultivars and broadening the genetic base of rice crop. In order to obtain new varieties of rice with improved agronomic and grain characteristics, gamma radiation (60Co) has been used to generate novel mutants of the Basmati rice. In this study rice cultivars; Basmati-370 and Basmati-Pak, were exposed to different doses of gamma radiations and stable mutants along with parents were studied for genomic diversity on the basis of molecular marker (AFLP). Morphological data showed that mutants of Basmati-370 performed well for yield and yield components and grain physical parameters whereas, the mutant EL-30-2-1 has extra long rain trait as compared to the parent (Basmati-Pak). The genetic variations determined through AFLP revealed a total of 282 scorable bands, out of which 108 (37.81%) were polymorphic. The number of fragments produced by various primers combinations ranged from 11 - 26 with an average of 17.63fragments per primer combination. Maximum 26 bands were amplified with P-AAG/M-CAG primer combination and minimum one band was amplified with P-ATG/M-CTA primer combination. Two groups of genotypes were detected; group-A had DM-1-30-3-99, DM-1-30-34-99 and EF-1-20-52-04 mutants along with parent Basmati-370, whereas the group-B contained EL-30-2-1 and parent Basmati-Pak. The results of AFLP analysis indicated that the rate of polymorphism was 4.43% (DM-1-30-3-99), 4.25% (DM-1-30-34-99) and 6.38% (EF-1-20-52-04) among the genomes of mutants and parent Basmati-370, respectively, whereas polymorphism rate was 5.32% between genome of EL-30-2-1 and Basmati-Pak. The study further confirmed that the use of gamma radiations is an effective approach for creating new rice germplasm

A step towards testing general relativity using weak gravitational lensing and redshift surveys

Using the linear theory of perturbations in General Relativity, we express a set of consistency relations that can be observationally tested with current and future large scale structure surveys. We then outline a stringent model-independent program to test gravity on cosmological scales. We illustrate the feasibility of such a program by jointly using several observables like peculiar velocities, galaxy clustering and weak gravitational lensing. After addressing possible observational or astrophysical caveats like galaxy bias and redshift uncertainties, we forecast in particular how well one can predict the lensing signal from a cosmic shear survey using an over-lapping galaxy survey. We finally discuss the specific physics probed this way and illustrate how $f(R)$ gravity models would fail such a test.Comment: 12 pages, 10 figure

Microbiota-produced indole metabolites disrupt mitochondrial function and inhibit Cryptosporidium parvum growth

Cryptosporidiosis is a leading cause of life-threatening diarrhea in young children in resource-poor settings. To explore microbial influences on susceptibility, we screened 85 microbiota-associated metabolites for their effects on Cryptosporidium parvum growth in vitro. We identify eight inhibitory metabolites in three main classes: secondary bile salts/acids, a vitamin