Catalysis by hen egg-white lysozyme proceeds via a covalent intermediate

Hen egg-white lysozyme (HEWL) was the first enzyme to have its three-dimensional structure determined by X-ray diffraction techniques(1). A catalytic mechanism, featuring a long-lived oxo-carbenium-ion intermediate, was proposed on the basis of model-building studies(2). The `Phillips' mechanism is widely held as the paradigm for the catalytic mechanism of beta -glycosidases that cleave glycosidic linkages with net retention of configuration of the anomeric centre. Studies with other retaining beta -glycosidases, however, provide strong evidence pointing to a common mechanism for these enzymes that involves a covalent glycosyl-enzyme intermediate, as previously postulated(3). Here we show, in three different cases using electrospray ionization mass spectrometry, a catalytically competent covalent glycosyl-enzyme intermediate during the catalytic cycle of HEWL. We also show the three-dimensional structure of this intermediate as determined by Xray diffraction. We formulate a general catalytic mechanism for all retaining beta -glycosidases that includes substrate distortion, formation of a covalent intermediate, and the electrophilic migration of C1 along the reaction coordinate

Disentangling astroglial physiology with a realistic cell model in silico

Electrically non-excitable astroglia take up neurotransmitters, buffer extracellular K+ and generate Ca2+ signals that release molecular regulators of neural circuitry. The underlying machinery remains enigmatic, mainly because the sponge-like astrocyte morphology has been difficult to access experimentally or explore theoretically. Here, we systematically incorporate multi-scale, tri-dimensional astroglial architecture into a realistic multi-compartmental cell model, which we constrain by empirical tests and integrate into the NEURON computational biophysical environment. This approach is implemented as a flexible astrocyte-model builder ASTRO. As a proof-of-concept, we explore an in silico astrocyte to evaluate basic cell physiology features inaccessible experimentally. Our simulations suggest that currents generated by glutamate transporters or K+ channels have negligible distant effects on membrane voltage and that individual astrocytes can successfully handle extracellular K+ hotspots. We show how intracellular Ca2+ buffers affect Ca2+ waves and why the classical Ca2+ sparks-and-puffs mechanism is theoretically compatible with common readouts of astroglial Ca2+ imaging

The ownership of digital infrastructure: Exploring the deployment of software libraries in a digital innovation cluster

Boundary resources have been shown to enable the arm’s-length relationships between platform owners and third-party developers that underlie digital innovation in platform ecosystems. While boundary resources that are owned by open-source communities and smaller-scale software vendors are also critical components in the digital infrastructure, their role in digital innovation has yet to be systematically explored. In particular, software libraries are popular boundary resources that provide functionality without the need for continued interaction with their owners. They are used extensively by commercial vendors to enable customization of their software products, by communities to disseminate open-source software, and by big-tech platform owners to provide functionality that does not involve control. This paper reports on the deployment of such software libraries in the web and mobile (Android) contexts by 107 startup companies in London. Our findings show that libraries owned by big-tech companies, product vendors, and communities coexist; that the deployment of big-tech libraries is unaffected by the scale of the deploying startup; and that context evolution paths are consequential for library deployment. These findings portray a balanced picture of digital infrastructure as neither the community-based utopia of early open-source research nor the dystopia of the recent digital dominance literature

What do we know and when do we know it?

Two essential aspects of virtual screening are considered: experimental design and performance metrics. In the design of any retrospective virtual screen, choices have to be made as to the purpose of the exercise. Is the goal to compare methods? Is the interest in a particular type of target or all targets? Are we simulating a ‘real-world’ setting, or teasing out distinguishing features of a method? What are the confidence limits for the results? What should be reported in a publication? In particular, what criteria should be used to decide between different performance metrics? Comparing the field of molecular modeling to other endeavors, such as medical statistics, criminology, or computer hardware evaluation indicates some clear directions. Taken together these suggest the modeling field has a long way to go to provide effective assessment of its approaches, either to itself or to a broader audience, but that there are no technical reasons why progress cannot be made

Women’s self-rated attraction to male faces does not correspond with physiological arousal

Data Availability Statement: The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.Peer reviewedPublisher PD

Gene Expression Analysis of In Vivo Fluorescent Cells

BACKGROUND: The analysis of gene expression for tissue homogenates is of limited value because of the considerable cell heterogeneity in tissues. However, several methods are available to isolate a cell type of interest from a complex tissue, the most reliable one being Laser Microdissection (LMD). Cells may be distinguished by their morphology or by specific antigens, but the obligatory staining often results in RNA degradation. Alternatively, particular cell types can be detected in vivo by expression of fluorescent proteins from cell type-specific promoters. METHODOLOGY/PRINCIPAL FINDINGS: We developed a technique for fixing in vivo fluorescence in brain cells and isolating them by LMD followed by an optimized RNA isolation procedure. RNA isolated from these cells was of equal quality as from unfixed frozen tissue, with clear 28S and 18S rRNA bands of a mass ratio of approximately 2ratio1. We confirmed the specificity of the amplified RNA from the microdissected fluorescent cells as well as its usefulness and reproducibility for microarray hybridization and quantitative real-time PCR (qRT-PCR). CONCLUSIONS/SIGNIFICANCE: Our technique guarantees the isolation of sufficient high quality RNA obtained from specific cell populations of the brain expressing soluble fluorescent marker, which is a critical prerequisite for subsequent gene expression studies by microarray analysis or qRT-PCR

Microarray identifies ADAM family members as key responders to TGF-β1 in alveolar epithelial cells

The molecular mechanisms of Idiopathic Pulmonary Fibrosis (IPF) remain elusive. Transforming Growth Factor beta 1(TGF-β1) is a key effector cytokine in the development of lung fibrosis. We used microarray and computational biology strategies to identify genes whose expression is significantly altered in alveolar epithelial cells (A549) in response to TGF-β1, IL-4 and IL-13 and Epstein Barr virus. A549 cells were exposed to 10 ng/ml TGF-β1, IL-4 and IL-13 at serial time points. Total RNA was used for hybridisation to Affymetrix Human Genome U133A microarrays. Each in vitro time-point was studied in duplicate and an average RMA value computed. Expression data for each time point was compared to control and a signal log ratio of 0.6 or greater taken to identify significant differential regulation. Using normalised RMA values and unsupervised Average Linkage Hierarchical Cluster Analysis, a list of 312 extracellular matrix (ECM) proteins or modulators of matrix turnover was curated via Onto-Compare and Gene-Ontology (GO) databases for baited cluster analysis of ECM associated genes. Interrogation of the dataset using ontological classification focused cluster analysis revealed coordinate differential expression of a large cohort of extracellular matrix associated genes. Of this grouping members of the ADAM (A disintegrin and Metalloproteinase domain containing) family of genes were differentially expressed. ADAM gene expression was also identified in EBV infected A549 cells as well as IL-13 and IL-4 stimulated cells. We probed pathologenomic activities (activation and functional activity) of ADAM19 and ADAMTS9 using siRNA and collagen assays. Knockdown of these genes resulted in diminished production of collagen in A549 cells exposed to TGF-β1, suggesting a potential role for these molecules in ECM accumulation in IPF

Understanding patient acceptance and refusal of HIV testing in the emergency department

<p>ABSTRACT</p> <p>Background</p> <p>Despite high rates of patient satisfaction with emergency department (ED) HIV testing, acceptance varies widely. It is thought that patients who decline may be at higher risk for HIV infection, thus we sought to better understand patient acceptance and refusal of ED HIV testing.</p> <p>Methods</p> <p>In-depth interviews with fifty ED patients (28 accepters and 22 decliners of HIV testing) in three ED HIV testing programs that serve vulnerable urban populations in northern California.</p> <p>Results</p> <p>Many factors influenced the decision to accept ED HIV testing, including curiosity, reassurance of negative status, convenience, and opportunity. Similarly, a number of factors influenced the decision to decline HIV testing, including having been tested recently, the perception of being at low risk for HIV infection due to monogamy, abstinence or condom use, and wanting to focus on the medical reason for the ED visit. Both accepters and decliners viewed ED HIV testing favorably and nearly all participants felt comfortable with the testing experience, including the absence of counseling. While many participants who declined an ED HIV test had logical reasons, some participants also made clear that they would prefer not to know their HIV status rather than face psychosocial consequences such as loss of trust in a relationship or disclosure of status in hospital or public health records.</p> <p>Conclusions</p> <p>Testing for HIV in the ED as for any other health problem reduces barriers to testing for some but not all patients. Patients who decline ED HIV testing may have rational reasons, but there are some patients who avoid HIV testing because of psychosocial ramifications. While ED HIV testing is generally acceptable, more targeted approaches to testing are necessary for this subgroup.</p

Modelling the public health impact of male circumcision for HIV prevention in high prevalence areas in Africa

Background: Recent clinical trials in Africa, in combination with several observational epidemiological studies, have provided evidence that male circumcision can reduce HIV female-to-male transmission risk by 60% or more. However, the public health impact of large-scale male circumcision programs for HIV prevention is unclear. Methods: Two mathematical models were examined to explore this issue: a random mixing model and a compartmental model that distinguishes risk groups associated with sex work. In the compartmental model, two scenarios were developed, one calculating HIV transmission and prevalence in a context similar to the country of Botswana, and one similar to Nyanza Province, in western Kenya. Results: In both models, male circumcision programs resulted in large and sustained declines in HIV prevalence over time among both men and women. Men benefited somewhat more than women, but prevalence among women was also reduced substantially. With 80% male circumcision uptake, the reductions in prevalence ranged from 45% to 67% in the two "countries", and with 50% uptake, from 25% to 41%. It would take over a decade for the intervention to reach its full effect. Conclusion: Large-scale uptake of male circumcision services in African countries with high HIV prevalence, and where male circumcision is not now routinely practised, could lead to substantial reductions in HIV transmission and prevalence over time among both men and women

Prime movers : mechanochemistry of mitotic kinesins

Mitotic spindles are self-organizing protein machines that harness teams of multiple force generators to drive chromosome segregation. Kinesins are key members of these force-generating teams. Different kinesins walk directionally along dynamic microtubules, anchor, crosslink, align and sort microtubules into polarized bundles, and influence microtubule dynamics by interacting with microtubule tips. The mechanochemical mechanisms of these kinesins are specialized to enable each type to make a specific contribution to spindle self-organization and chromosome segregation