Structures of EccB\u3csub\u3e1\u3c/sub\u3e and EccD\u3csub\u3e1\u3c/sub\u3e from the Core Complex of the Mycobacterial ESX-1 Type VII Secretion System

Background: The ESX-1 type VII secretion system is an important determinant of virulence in pathogenic mycobacteria, including Mycobacterium tuberculosis. This complicated molecular machine secretes folded proteins through the mycobacterial cell envelope to subvert the host immune response. Despite its important role in disease very little is known about the molecular architecture of the ESX-1 secretion system. Results: This study characterizes the structures of the soluble domains of two conserved core ESX-1 components – EccB1 and EccD1. The periplasmic domain of EccB1 consists of 4 repeat domains and a central domain, which together form a quasi 2-fold symmetrical structure. The repeat domains of EccB1 are structurally similar to a known peptidoglycan binding protein suggesting a role in anchoring the ESX-1 system within the periplasmic space. The cytoplasmic domain of EccD1has a ubiquitin-like fold and forms a dimer with a negatively charged groove. Conclusions: These structures represent a major step towards resolving the molecular architecture of the entire ESX-1 assembly and may contribute to ESX-1 targeted tuberculosis intervention strategies

25th annual computational neuroscience meeting: CNS-2016

The same neuron may play different functional roles in the neural circuits to which it belongs. For example, neurons in the Tritonia pedal ganglia may participate in variable phases of the swim motor rhythms [1]. While such neuronal functional variability is likely to play a major role the delivery of the functionality of neural systems, it is difficult to study it in most nervous systems. We work on the pyloric rhythm network of the crustacean stomatogastric ganglion (STG) [2]. Typically network models of the STG treat neurons of the same functional type as a single model neuron (e.g. PD neurons), assuming the same conductance parameters for these neurons and implying their synchronous firing [3, 4]. However, simultaneous recording of PD neurons shows differences between the timings of spikes of these neurons. This may indicate functional variability of these neurons. Here we modelled separately the two PD neurons of the STG in a multi-neuron model of the pyloric network. Our neuron models comply with known correlations between conductance parameters of ionic currents. Our results reproduce the experimental finding of increasing spike time distance between spikes originating from the two model PD neurons during their synchronised burst phase. The PD neuron with the larger calcium conductance generates its spikes before the other PD neuron. Larger potassium conductance values in the follower neuron imply longer delays between spikes, see Fig. 17.Neuromodulators change the conductance parameters of neurons and maintain the ratios of these parameters [5]. Our results show that such changes may shift the individual contribution of two PD neurons to the PD-phase of the pyloric rhythm altering their functionality within this rhythm. Our work paves the way towards an accessible experimental and computational framework for the analysis of the mechanisms and impact of functional variability of neurons within the neural circuits to which they belong

Accuracy of Digital Indirect Bonding Using Different Bracket Transfer Methods and a Novel Tray Material

Accurate bracket placement is essential for successful orthodontic treatment. The indirect bonding (IDB) technique was developed to overcome errors found in direct bonding. IDB provides advantages of minimized patient discomfort, improved visualization of teeth, and reduction of wire bending. Digital IDB techniques now include intra-oral scanning, 3D printing, and IDB software. Studies have repeatedly shown the high transfer accuracy of silicone IDB trays. 3D printed IDB trays are a time saving alternative with comparable accuracy to silicone trays. To utilize the benefits of both materials, a novel shape memory polymer (SMP) Tera Harz TC-85DAC has been proposed as a digital IDB material for this study. The objective of this study is to evaluate the bracket transfer accuracy of three distinct digital IDB techniques: 3D printed resin, CAD driven silicone, and 3D printed shape-memory polymer (SMP) trays. 15 maxillary and 15 mandibular intra-orally scanned arches of pre-existing University of Illinois Chicago (UIC) Orthodontic Department were used for the study. Brackets were semi-automatically placed on each arch following the digitally fabricated facial axis (FA) point. 30 IDB transfer trays were produced for each material: 3D printed resin (“bar”), CAD driven silicone (“silicone”), and 3D printed (“SMP”) for a total of 90 transfer trays. IDB was performed for each technique and bracketed models were scanned for superimposition to test accuracy in the linear (mesiodistal, occluso-gingival, and bucco-lingual) and angular (torque, rotation, and tip) dimensions. A one-sample t-test was conducted to assess for any significant error in bracket placement in the three materials. A repeated measures ANOVA, with Greenhouse-Geisser correction, was conducted to assess whether there were mean differences between the three techniques in the linear and angular dimension. The results of our study showed that the bar material had the greatest frequency of bracket placement errors. Premolars had the greatest frequency of bracket placement errors specifically with the bar technique. Overall, the SMP technique had the greatest accuracy in linear and angular dimensions when compared to the bar and silicone method. The standard for clinical acceptability was set to <0.5mm and <2 degrees. All methods were clinically acceptable in the linear directions and all methods were not clinically acceptable in the angular measurements. The SMP resin material shows promising results as a novel IDB tray material. Further investigation is needed to develop the SMP material to be compatible with in vivo testing. In addition, future studies are needed to evaluate transfer tray design to control deviations in the angular dimensions. By mastering the indirect bonding technique, orthodontists will successfully streamline the clinical workflow, reduce costs, and ultimately increase patient satisfaction

The effects of preference assessment type on problem behavior

Individuals with intellectual and developmental disabilities who engage in problem behavior maintained by access to tangibles may exhibit more problem behavior during certain preference assessments. We compared three common preference assessments to determine which resulted in fewer problem behaviors. The paired stimulus and multiple-stimulus without replacement assessments produced higher rates of problem behavior than the free operant (FO) assessment, suggesting that the FO assessment may be the most appropriate assessment for individuals who engage in problem behavior maintained by access to tangibles

Structures of EccB1 and EccD1 from the core complex of the mycobacterial ESX-1 type VII secretion system.

BackgroundThe ESX-1 type VII secretion system is an important determinant of virulence in pathogenic mycobacteria, including Mycobacterium tuberculosis. This complicated molecular machine secretes folded proteins through the mycobacterial cell envelope to subvert the host immune response. Despite its important role in disease very little is known about the molecular architecture of the ESX-1 secretion system.ResultsThis study characterizes the structures of the soluble domains of two conserved core ESX-1 components - EccB1 and EccD1. The periplasmic domain of EccB1 consists of 4 repeat domains and a central domain, which together form a quasi 2-fold symmetrical structure. The repeat domains of EccB1 are structurally similar to a known peptidoglycan binding protein suggesting a role in anchoring the ESX-1 system within the periplasmic space. The cytoplasmic domain of EccD1has a ubiquitin-like fold and forms a dimer with a negatively charged groove.ConclusionsThese structures represent a major step towards resolving the molecular architecture of the entire ESX-1 assembly and may contribute to ESX-1 targeted tuberculosis intervention strategies

Structural Variability of EspG Chaperones from Mycobacterial ESX-1, ESX-3, and ESX-5 Type VII Secretion Systems.

Type VII secretion systems (ESX) are responsible for transport of multiple proteins in mycobacteria. How different ESX systems achieve specific secretion of cognate substrates remains elusive. In the ESX systems, the cytoplasmic chaperone EspG forms complexes with heterodimeric PE-PPE substrates that are secreted from the cells or remain associated with the cell surface. Here we report the crystal structure of the EspG1 chaperone from the ESX-1 system determined using a fusion strategy with T4 lysozyme. EspG1 adopts a quasi 2-fold symmetric structure that consists of a central β-sheet and two α-helical bundles. In addition, we describe the structures of EspG3 chaperones from four different crystal forms. Alternate conformations of the putative PE-PPE binding site are revealed by comparison of the available EspG3 structures. Analysis of EspG1, EspG3, and EspG5 chaperones using small-angle X-ray scattering reveals that EspG1 and EspG3 chaperones form dimers in solution, which we observed in several of our crystal forms. Finally, we propose a model of the ESX-3 specific EspG3-PE5-PPE4 complex based on the small-angle X-ray scattering analysis

Structural Variability of EspG Chaperones from Mycobacterial ESX-1, ESX-3, and ESX-5 Type VII Secretion Systems

Type VII secretion systems (ESX) are responsible for transport of multiple proteins in mycobacteria. How different ESX systems achieve specific secretion of cognate substrates remains elusive. In the ESX systems, the cytoplasmic chaperone EspG forms complexes with heterodimeric PE–PPE substrates that are secreted from the cells or remain associated with the cell surface. Here we report the crystal structure of the EspG1 chaperone from the ESX-1 system determined using a fusion strategy with T4 lysozyme. EspG$_1$ adopts a quasi 2-fold symmetric structure that consists of a central β-sheet and two α-helical bundles. In addition, we describe the structures of EspG3 chaperones from four different crystal forms. Alternate conformations of the putative PE–PPE binding site are revealed by comparison of the available EspG$_3$ structures. Analysis of EspG$_1$, EspG$_3$, and EspG$_5$ chaperones using small-angle X-ray scattering reveals that EspG$_1$ and EspG$_3$ chaperones form dimers in solution, which we observed in several of our crystal forms. Finally, we propose a model of the ESX-3 specific EspG$_3$–PE5–PPE4 complex based on the small-angle X-ray scattering analysis