Biogenesis of a Bacterial Organelle: The Carboxysome Assembly Pathway

SummaryThe carboxysome is a protein-based organelle for carbon fixation in cyanobacteria, keystone organisms in the global carbon cycle. It is composed of thousands of subunits including hexameric and pentameric proteins that form a shell to encapsulate the enzymes ribulose 1,5-bisphosphate carboxylase/oxygenase and carbonic anhydrase. Here, we describe the stages of carboxysome assembly and the requisite gene products necessary for progression through each. Our results demonstrate that, unlike membrane-bound organelles of eukaryotes, in carboxysomes the interior of the compartment forms first, at a distinct site within the cell. Subsequently, shell proteins encapsulate this procarboxysome, inducing budding and distribution of functional organelles within the cell. We propose that the principles of carboxysome assembly that we have uncovered extend to diverse bacterial microcompartments

Optimization of an Air Core Dual Halbach Array Axial Flux Rim Drive for Electric Aircraft

The anticipated development of the on-demand-mobility (ODM) market has accelerated the development of electric aircraft. Most proposed electric aircraft have propulsion systems that consist of fans directly driven by electric motors. The lower complexity of these propulsion systems opens the door to more custom propulsion system designs that are tailored to a given aircraft and its mission. This paper represents initial steps in the development of an electric propulsion system design code. A proof of concept version of the code is presented. The proof of concept version of the code is for the design of an axial flux rim driven propulsion system. NASA's all electric aircraft X-57, is used as a case study for this design code. The results of this case study are used to discuss the feasibility and potential benefits of using an axial flux rim driven propulsor on X-57. The final result of the case study shows a potential 4km increase in range over the current design

Plant Glutathione Biosynthesis: Diversity in Biochemical Regulation and Reaction Products

In plants, exposure to temperature extremes, heavy metal-contaminated soils, drought, air pollutants, and pathogens results in the generation of reactive oxygen species that alter the intracellular redox environment, which in turn influences signaling pathways and cell fate. As part of their response to these stresses, plants produce glutathione. Glutathione acts as an anti-oxidant by quenching reactive oxygen species, and is involved in the ascorbate–glutathione cycle that eliminates damaging peroxides. Plants also use glutathione for the detoxification of xenobiotics, herbicides, air pollutants (sulfur dioxide and ozone), and toxic heavy metals. Two enzymes catalyze glutathione synthesis: glutamate–cysteine ligase, and glutathione synthetase. Glutathione is a ubiquitous protective compound in plants, but the structural and functional details of the proteins that synthesize it, as well as the potential biochemical mechanisms of their regulation, have only begun to be explored. As discussed here, the core reactions of glutathione synthesis are conserved across various organisms, but plants have diversified both the regulatory mechanisms that control its synthesis and the range of products derived from this pathway. Understanding the molecular basis of glutathione biosynthesis and its regulation will expand our knowledge of this component in the plant stress response network

Biochemical characterization of predicted Precambrian RuBisCO

The antiquity and global abundance of the enzyme, RuBisCO, attests to the crucial and longstanding role it has played in the biogeochemical cycles of Earth over billions of years. The counterproductive oxygenase activity of RuBisCO has persisted over billions of years of evolution, despite its competition with the carboxylase activity necessary for carbon fixation, yet hypotheses regarding the selective pressures governing RuBisCO evolution have been limited to speculation. Here we report the resurrection and biochemical characterization of ancestral RuBisCOs, dating back to over one billion years ago (Gyr ago). Our findings provide an ancient point of reference revealing divergent evolutionary paths taken by eukaryotic homologues towards improved specificity for CO2, versus the evolutionary emphasis on increased rates of carboxylation observed in bacterial homologues. Consistent with these distinctions, in vivo analysis reveals the propensity of ancestral RuBisCO to be encapsulated into modern-day carboxysomes, bacterial organelles central to the cyanobacterial CO2 concentrating mechanism

Colour scales with climate in North American ratsnakes: a test of the thermal melanism hypothesis using community science images

Animal colour is a complex trait shaped by multiple selection pressures that can vary across geography. The thermal melanism hypothesis predicts that darker coloration is beneficial to animals in colder regions because it allows for more rapid solar absorption. Here, we use community science images of three closely related species of North American ratsnakes (genus Pantherophis) to examine if climate predicts colour variation across range-wide scales. We predicted that darker individuals are found in colder regions and higher elevations, in accordance with the thermal melanism hypothesis. Using an unprecedented dataset of over 8000 images, we found strong support for temperature as a key predictor of darker colour, supporting thermal melanism. We also found that elevation and precipitation are predictive of colour, but the direction and magnitude of these effects were more variable across species. Our study is the first to quantify colour variation in Pantherophis ratsnakes, highlighting the value of community science images for studying range-wide colour variation

NLL′{'} resummation of jet mass

Starting from a factorization theorem in effective field theory, we present resummed results for two non-global observables: the invariant-mass distribution of jets and the energy distribution outside jets. Our results include the full next-to-leading-order corrections to the hard, jet and soft functions and are implemented in a parton-shower framework which generates the renormalization-group running in the effective theory. The inclusion of these matching corrections leads to an improved description of the data and reduced theoretical uncertainties. They will have to be combined with two-loop running in the future, but our results are an important first step towards the higher-logarithmic resummation of non-global observables.Comment: 32 pages, 12 figures. v2: journal versio

Microscope 2.0: An Augmented Reality Microscope with Real-time Artificial Intelligence Integration

The brightfield microscope is instrumental in the visual examination of both biological and physical samples at sub-millimeter scales. One key clinical application has been in cancer histopathology, where the microscopic assessment of the tissue samples is used for the diagnosis and staging of cancer and thus guides clinical therapy. However, the interpretation of these samples is inherently subjective, resulting in significant diagnostic variability. Moreover, in many regions of the world, access to pathologists is severely limited due to lack of trained personnel. In this regard, Artificial Intelligence (AI) based tools promise to improve the access and quality of healthcare. However, despite significant advances in AI research, integration of these tools into real-world cancer diagnosis workflows remains challenging because of the costs of image digitization and difficulties in deploying AI solutions. Here we propose a cost-effective solution to the integration of AI: the Augmented Reality Microscope (ARM). The ARM overlays AI-based information onto the current view of the sample through the optical pathway in real-time, enabling seamless integration of AI into the regular microscopy workflow. We demonstrate the utility of ARM in the detection of lymph node metastases in breast cancer and the identification of prostate cancer with a latency that supports real-time workflows. We anticipate that ARM will remove barriers towards the use of AI in microscopic analysis and thus improve the accuracy and efficiency of cancer diagnosis. This approach is applicable to other microscopy tasks and AI algorithms in the life sciences and beyond

A Two Micron All-Sky Survey View of the Sagittarius Dwarf Galaxy: II. Swope Telescope Spectroscopy of M Giant Stars in the Dynamically Cold Sagittarius Tidal Stream

We present moderate resolution (~6 km/s) spectroscopy of 284 M giant candidates selected from the Two Micron All Sky Survey photometry. Radial velocities (RVs) are presented for stars mainly in the south, with a number having positions consistent with association to the trailing tidal tail of the Sagittarius (Sgr) dwarf galaxy. The latter show a clear RV trend with orbital longitude, as expected from models of the orbit and destruction of Sgr. A minimum 8 kpc width of the trailing stream about the Sgr orbital midplane is implied by verified RV members. The coldness of this stream (dispersion ~10 km/s) provides upper limits on the combined contributions of stream heating by a lumpy Galactic halo and the intrinsic dispersion of released stars, which is a function of the Sgr core mass. The Sgr trailing arm is consistent with a Galactic halo containing one dominant, LMC-like lump, however some lumpier halos are not ruled out. An upper limit to the total M/L of the Sgr core is 21 in solar units. A second structure that roughly mimics expectations for wrapped, leading Sgr arm debris crosses the trailing arm in the Southern Hemisphere; however, this may also be an unrelated tidal feature. Among the <13 kpc M giants toward the South Galactic Pole are some with large RVs that identify them as halo stars, perhaps part of the Sgr leading arm near the Sun. The positions and RVs of Southern Hemisphere M giants are compared with those of southern globular clusters potentially stripped from the Sgr system and support for association of Pal 2 and Pal 12 with Sgr debris is found. Our discussion includes description of a masked-filtered cross-correlation methodology that achieves better than 1/20 of a resolution element RVs in moderate resolution spectra.Comment: 41 pages, 6 figures, Astronomical Journal, in press (submitted Nov. 24, 2003; tentatively scheduled for July 2004 issue

CD23 expression in mantle cell lymphoma is associated with CD200 expression, leukemic non-nodal form, and a better prognosis

Mantle cell lymphoma (MCL) is usually CD23 negative, a feature helpful in distinguishing MCL from chronic lymphocytic leukemia/small lymphocytic lymphoma. However, a subset of MCL cases can be CD23+. Limited data are available regarding the clinicopathological features and prognosis of patients with CD23+ MCL. In this study, we reviewed 798 cases of MCL and identified 103 (13%) that were CD23+ by flow cytometry, all of which were positive for cyclin D1 and/or associated with CCND1/IGH. In all cases of CD23+ MCL, CD23 expression was dim partial or dim, unlike moderate to bright CD23 expression observed in chronic lymphocytic leukemia/small lymphocytic lymphoma. The clinicopathological features and outcome of patients with CD23+ MCL were compared with 240 patients with typical MCL negative for CD23. Patients with CD23+ MCL more often had an elevated leukocyte count (33% versus 18%, P = .009), bone marrow involvement (89% versus 78%, P = .02), stage 4 disease (87% versus 77%, P = .03), and a leukemic presentation (42% versus 11%, P = .0001). CD23+ MCL was also more often positive for CD200 (17% versus. 4.6%, P = .0005) and less commonly positive for SOX11 (55% versus. 74%, P = .027). All other clinicopathological features were similar. With similar treatment regimens and observation times, patients with CD23+ MCL had a significant better overall survival (P = .02) and progression-free survival (P = .029). In conclusion, CD23 expression was observed in 13% of MCL cases and is associated with a better prognosis in patients with MCL. CD23 is associated with leukocytosis, a leukemic presentation, bone marrow involvement, CD200 expression, and a lower frequency of SOX11 positivity