Oxford Molecular Motors

Abstract:

The bacterial flagellum is a macromolecular protein complex that enables motility in many species. Bacterial flagella self-assemble a strong, multicomponent drive shaft that couples rotation in the inner membrane to the micrometre-long flagellar filament that powers bacterial swimming in viscous fluids^1-3. Here, we present structures of the intact Salmonella flagellar basal body⁴, encompassing the inner membrane rotor, drive shaft and outer-membrane bushing, solved using cryo-electron microscopy to resolutions of 2.2-3.7 Å. The structures reveal molecular details of how 173 protein molecules of 13 different types assemble into a complex spanning two membranes and a cell wall. The helical drive shaft at one end is intricately interwoven with the rotor component with both the export gate complex and the proximal rod forming interactions with the MS-ring. At the other end, the drive shaft distal rod passes through the LP-ring bushing complex, which functions as a molecular bearing anchored in the outer membrane through interactions with the lipopolysaccharide. The in situ structure of a protein complex capping the drive shaft provides molecular insights into the assembly process of this molecular machine.

Abstract:

The article describes a complex study of detonation nanodiamonds (DND) aqueous dispersions. In this research, DND sample was characterised by means of IR, NMR spectroscopy, TEM, thermogravimetric analysis, size distribution, and ζ-potentials. It was shown that DND sample includes several surface groups, mainly hydroxylic, carboxylic, and carbonyl ones. Dynamic light scattering results revealed that in the concentration range C = 0.002–0.3 wt%, DND nanoparticles size is equal to 55 ± 5 nm. It was demonstrated that DND possessed weak antiradical activity, had an inhibitory effect on F1F0-ATPase activity, almost did not affect platelet aggregation, formed a stronger complex with human serum albumin (HSA) in subdomain IB (digitoxin, Kb = 20.0 ± 2.4 l·g−1) and a less strong complex in subdomain IIA (warfarin, Kb = 3.7 ± 0.1 l·g−1), inhibited the esterase activity of HSA, DND dispersions (C = 0.0012–0.15 wt%) revealed genotoxic effect towards PBMCs, did not affect cellular proliferation in the experiment with HEK293 cell line, did not reveal cytotoxic effect up to 0.01 wt%. Using DFT and MD approaches allowed us to perform a simulation of interaction between DND nanoparticle and water molecules.

Abstract:

We study the large-scale anisotropy of the universe by measuring the dipole in the angular distribution of a flux-limited, all-sky sample of 1.36 million quasars observed by the Wide-field Infrared Survey Explorer (WISE). This sample is derived from the new CatWISE2020 catalog, which contains deep photometric measurements at 3.4 and 4.6 μm from the cryogenic, post-cryogenic, and reactivation phases of the WISE mission. While the direction of the dipole in the quasar sky is similar to that of the cosmic microwave background (CMB), its amplitude is over twice as large as expected, rejecting the canonical, exclusively kinematic interpretation of the CMB dipole with a p-value of 5 × 10−7 (4.9σ for a normal distribution, one-sided), the highest significance achieved to date in such studies. Our results are in conflict with the cosmological principle, a foundational assumption of the concordance ΛCDM model.

Abstract:

Regulatory switches are wide spread in many biological systems. Uniquely among them, the switch of the bacterial flagellar motor is not an on/off switch but rather controls the motor's direction of rotation in response to binding of the signaling protein CheY. Despite its extensive study, the molecular mechanism underlying this switch has remained largely unclear. Here, we resolved the functions of each of the three CheY-binding sites at the switch in E. coli, as well as their different dependencies on phosphorylation and acetylation of CheY. Based on this, we propose that CheY motor switching activity is potentiated upon binding to the first site. Binding of potentiated CheY to the second site produces unstable switching and at the same time enables CheY binding to the third site, an event that stabilizes the switched state. Thereby, this mechanism exemplifies a unique combination of tight motor regulation with inherent switching flexibility.

Abstract:

We study the behaviour of the green alga Chlamydomonas reinhardtii (CR) in the presence of neighbouring regions of different viscosity. We show that the velocity and angular diffusion of the algae decreases when the viscosity of the surrounding medium is increased. We report on a phenomenon occurring when the algae try to cross from a region of low viscosity to a highly viscous one, which causes CR to re-orient and scatter away from the interface if it is approached at a sufficiently small angle. We highlight that the effect does not occur for CR crossing from high to low viscosity regions. Lastly we show that algae do not concentrate in the region of high viscosity despite them swimming slower there. On the contrary, they concentrate in the region of low viscosity or maintain a uniform concentration profile, depending on the viscosity ratio between the two regions.