HisE11 and HisF8 Provide Bis-histidyl Heme Hexa-coordination in the Globin Domain of Geobacter sulfurreducens Globin-coupled Sensor

Among heme-based sensors, recent phylogenomic and sequence analyses have identified 34 globin coupled sensors (GCS), to which an aerotactic or gene-regulating function has been tentatively ascribed. Here, the structural and biochemical characterization of the globin domain of the GCS from Geobacter sulfurreducens (GsGCS¹⁶²) is reported. A combination of X-ray crystallography (crystal structure at 1.5 Å resolution), UV-vis and resonance Raman spectroscopy reveals the ferric GsGCS¹⁶² as an example of bis-histidyl hexa-coordinated GCS. In contrast to the known hexa-coordinated globins, the distal heme-coordination in ferric GsGCS¹⁶² is provided by a His residue unexpectedly located at the E11 topological site. Furthermore, UV-vis and resonance Raman spectroscopy indicated that ferrous deoxygenated GsGCS¹⁶² is a penta-/hexa-coordinated mixture, and the heme hexa-to-penta-coordination transition does not represent a rate-limiting step for carbonylation kinetics. Lastly, electron paramagnetic resonance indicates that ferrous nitrosylated GsGCS¹⁶² is a penta-coordinated species, where the proximal HisF8-Fe bond is severed.     

FtsZ-less cell division in archaea and bacteria

A dedicated cell division machinery is needed for efficient proliferation of an organism. The eukaryotic actin-myosin based mechanism and the bacterial FtsZ-dependent machinery have both been characterized in detail, and a third division mechanism, the Cdv system, was recently discovered in archaea from the Crenarchaeota phylum. Despite these findings, division mechanisms remain to be identified in, for example, organisms belonging to the bacterial PVC superphylum, bacteria with extremely reduced genomes, wall-less archaea and bacteria, and in archaea that carry out the division process without cell constriction. Cytokinesis mechanisms in these clades and individual taxa are likely to include adaptation of host functions to division of bacterial symbionts, transfer of bacterial division genes into the host genome, vesicle formation without a dedicated constriction machinery, cross-wall formation without invagination, as well as entirely novel division mechanisms.     

Computational fluid dynamics analysis of drag and convective heat transfer of individual body segments for different cyclist positions

This study aims at investigating drag and convective heat transfer for cyclists at a high spatial resolution. Such an increased spatial resolution, when combined with flow-field data, can increase insight in drag reduction mechanisms and in the thermo-physiological response of cyclists related to heat stress and hygrothermal performance of clothing. Computational fluid dynamics (steady Reynolds-averaged Navier-Stokes) is used to evaluate the drag and convective heat transfer of 19 body segments of a cyclist for three different cyclist positions. The influence of wind speed on the drag is analysed, indicating a pronounced Reynolds number dependency on the drag, where more streamlined positions show a dependency up to higher Reynolds numbers. The drag and convective heat transfer coefficient (CHTC) of the body segments and the entire cyclist are compared for all positions at racing speeds, showing high drag values for the head, legs and arms and high CHTCs for the legs, arms, hands and feet. The drag areas of individual body segments differ markedly for different cyclist positions whereas the convective heat losses of the body segments are found to be less sensitive to the position. CHTC-wind speed correlations are derived, in which the power-law exponent does not differ significantly for the individual body segments for all positions, where an average value of 0.84 is found. Similar CFD studies can be performed to assess drag and CHTCs at a higher spatial resolution for applications in other sport disciplines, bicycle equipment design or to assess convective moisture transfer.     

Synthesis and in vitro muscarinic activities of a series of 1,3-diazacycloalkyl carboxaldehyde oxime derivatives

A series of 1,3-diazacycloalkyl carboxaldehyde oxime derivatives was synthesized and tested for muscarinic activity in receptor binding assays using [3H]-oxotremorine-M (OXO-M) and [3H]-pirenzepine (PZ) as ligands. Potential muscarinic agonistic or antagonistic properties of the compounds were determined using binding studies measuring their potencies to inhibit the binding of OXO-M and PZ. Preferential inhibition of OXO-M binding was used as an indicator for potential muscarinic agonistic properties; this potential was confirmed in functional studies on isolated organs.     

Emerging viral infections in a rapidly changing world

Emerging viral infections in both humans and animals have been reported with increased frequency in recent years. Recent advances have been made in our knowledge of some of these, including severe acute respiratory syndrome-associated coronavirus, influenza A virus, human metapneumovirus, West Nile virus and Ebola virus. Research efforts to mitigate their effects have concentrated on improved surveillance and diagnostic capabilities, as well as on the development of vaccines and antiviral agents. More attention needs to be given to the identification of the underlying causes for the emergence of infectious diseases, which are often related to anthropogenic social and environmental changes. Addressing these factors might help to decrease the rate of emergence of infectious diseases and allow the transition to a more sustainable society.     

Exploring new methods and materials for enantioselective separations and catalysis

In this article, we will review and highlight some recent computational work on enantioselective adsorption and catalysis in zeolites and metal–organic frameworks. The design, development and understanding of chiral structures will help expand the utility of nanoporous materials into chiral technology. The highlighted works are examples of how molecular simulations can provide a fundamental understanding of chirality in nanoporous materials. This understanding is essential to help in the design and development of next-generation enantioselective separation devices and catalysts.     

A plant cell division algorithm based on cell biomechanics and ellipse-fitting

Background and Aims

The importance of cell division models in cellular pattern studies has been acknowledged since the 19th century. Most of the available models developed to date are limited to symmetric cell division with isotropic growth. Often, the actual growth of the cell wall is either not considered or is updated intermittently on a separate time scale to the mechanics. This study presents a generic algorithm that accounts for both symmetrically and asymmetrically dividing cells with isotropic and anisotropic growth. Actual growth of the cell wall is simulated simultaneously with the mechanics.

Methods

The cell is considered as a closed, thin-walled structure, maintained in tension by turgor pressure. The cell walls are represented as linear elastic elements that obey Hooke''s law. Cell expansion is induced by turgor pressure acting on the yielding cell-wall material. A system of differential equations for the positions and velocities of the cell vertices as well as for the actual growth of the cell wall is established. Readiness to divide is determined based on cell size. An ellipse-fitting algorithm is used to determine the position and orientation of the dividing wall. The cell vertices, walls and cell connectivity are then updated and cell expansion resumes. Comparisons are made with experimental data from the literature.

Key Results

The generic plant cell division algorithm has been implemented successfully. It can handle both symmetrically and asymmetrically dividing cells coupled with isotropic and anisotropic growth modes. Development of the algorithm highlighted the importance of ellipse-fitting to produce randomness (biological variability) even in symmetrically dividing cells. Unlike previous models, a differential equation is formulated for the resting length of the cell wall to simulate actual biological growth and is solved simultaneously with the position and velocity of the vertices.

Conclusions

The algorithm presented can produce different tissues varying in topological and geometrical properties. This flexibility to produce different tissue types gives the model great potential for use in investigations of plant cell division and growth in silico.