137 research outputs found
Mechanism for Vipp1 spiral formation, ring biogenesis, and membrane repair
No full textThe ESCRT-III-like protein Vipp1 couples filament polymerization with membrane remodeling. It assembles planar sheets as well as 3D rings and helical polymers, all implicated in mitigating plastid-associated membrane stress. The architecture of Vipp1 planar sheets and helical polymers remains unknown, as do the geometric changes required to transition between polymeric forms. Here we show how cyanobacterial Vipp1 assembles into morphologically-related sheets and spirals on membranes in vitro. The spirals converge to form a central ring similar to those described in membrane budding. Cryo-EM structures of helical filaments reveal a close geometric relationship between Vipp1 helical and planar lattices. Moreover, the helical structures reveal how filaments twist—a process required for Vipp1, and likely other ESCRT-III filaments, to transition between planar and 3D architectures. Overall, our results provide a molecular model for Vipp1 ring biogenesis and a mechanism for Vipp1 membrane stabilization and repair, with implications for other ESCRT-III systems
Mechanism for Vipp1 spiral formation, ring biogenesis and membrane repair
No full textHere, we collect an image dataset of Vipp1 polymerization dynamics on supported lipid bilayers using atomic force microscopy (AFM). A JPK NanoWizard Ultraspeed AFM (Bruker and JPK BioAFM) equipped with USC-F0.3-k0.3-10 cantilevers with spring constant of 0.3N nm−1, resonance frequency of about 300 kHz (Nanoworld), was employed for image acquisition. The AFM was operated in tapping mode with a cantilever oscillation frequency near to 150kHz. Both topographic and phase images were analysed using JPKSPM Data Processing, ImageJ, and WSxM software.Peer reviewe
Heterologous expression and in-vitro analysis of Streptococcus pneumoniae FtsEX divisome complex with peptidoglycan (PG) hydrolase PcsB and actin homologue FtsA, required for PG remodelling and cell separation
No full textBacterial cell division is orchestrated by the divisome complex of proteins necessary for new peptidoglycan (PG) synthesis and PG remodeling during septum formation and cell separation. These proteins have homologues in both Grampositive and Gram-negative species highlighting their fundamental biological role. The complex between FtsE and FtsX is recruited to the divisome at an early stage in mid-cell division and is required in assembling further downstream divisome proteins as well as in regulating divisome activity. Specifically, it provides a membrane anchor for an extracellular hydrolase that is required for hydrolysis of PG of old cell wall material and to enable separation of daughter cells during division.
In our heterologous expression study, we observed aberrant cell division defects in Escherichia coli (Ec) cell when subject to expression of the Streptococcus pneumoniae (Sp) FtsEX mimicking the phenotype of existing antibiotics. This phenotype can be rescued co-overexpressing SpFtsEX with its cognate peptidoglycan hydrolase; PcsB that hydrolyses Escherichia coli PG required for PG remodeling during cell separation. In this study, we have demonstrated Streptococcus pneumoniae FtsEX-FtsA and FtsEX-PcsB complexes can be isolated in-vitro using nanodiscs styrene-maleic-acid-lipid-particles (SMALP), preserving their membrane lipid environment. The protein-protein interaction studies indicate SpFtsX but not SpFtsE, interacts with the essential divisome protein SpFtsA, and PcsB successfully docks with FtsEX in the SMALP disk. Negative stain electron microscopy images and initial high resolution cryo-EM trials with these complexes indicates these tools could be prerequisite for investigating mechanistic insight about their structural-functional relationship and for further inhibitor screens for these complexes
Separator-free Zn-ion Battery with Mn:V<sub>3</sub>O<sub>7</sub>·H<sub>2</sub>O Nanobelts and a Zn<sup>2+</sup>-Polyacrylamide Semisolid Electrolyte with Ultralong Cycle Life
No full textVanadium based oxides are immensely suitable for zinc-ion-batteries
(ZIBs) due to their layered and stable crystal structures. In this
study, Mn doped V3O7·H2O nanobelts
were synthesized and used as cathodes in ZIBs for the very first time
and the doped oxide exhibited an enhanced capacity of 258 mAh g–1 compared to its undoped counterpart (208 mAh g–1) at the same current density of 40 mA g–1. Mn:V3O7·H2O outperforms the
V3O7·H2O due to the superior
bulk electrical conductivity as well as higher nanoscale current carrying
capability imparted by a high proportion of mixed valent states of
Mn3+, Mn2+, V5+, and V4+ and the smaller crystallite size that affords short diffusion lengths
for Zn2+ ions. The Mn:V3O7·H2O cathode is coupled with a Zn2+ ion conducting
polyacrylamide gel electrolyte and a Zn flakes/activated carbon (Zn
Fs/C) composite anode to yield a unique separator free Mn:V3O7·H2O/Zn2+-PAM gel/Zn-Fs/C
battery. The cell exhibits a capacity of ∼205 mAh g–1 (at 40 mA g–1) and retains 99% of its original
capacity after 3500 cycles. The Zn2+-PAM gel shows a high
ionic conductivity in the range of 5.9 to 28.2 S cm–1, over a wide temperature span of 0 to 70 °C, and a wide electrochemical
potential stability window of −0.5 to +2.3 V, thus rendering
it suitable for low temperature applications as well. The gel also
inhibits dendritic growth of Zn over the Zn-Fs/C anode through regulated
flow of Zn2+ ions during charging, prevents cathode dissolution,
and improves cycle life via preservation of structural integrity of
the Mn:V3O7·H2O cathode after
200 charge–discharge cycles. This is a highly scalable cell
configuration and opens up opportunities to produce long lasting batteries
completely free of costly separators with a semisolid free-standing
electrolyte and a robust doped oxide
ZnV 2 O 4 ‐Textured Carbon Composite Contacting a ZIF‐8 MOF Layer for a High Performance Non‐Aqueous Zinc‐Ion Battery
No full textNon-aqueous zinc-ion battery (ZIB) comprising a zinc vanadate@textured carbon (ZnV2O4@TC) composite cathode and Zn-anode demonstrates an improved Zn(II)-ion storage response, in terms of cyclability (230 mAh g−1 after 200 cycles, 84.9 % retention) and rate capability compared to pristine ZnV2O4 (175 mAh g−1 after 200 cycles, 45.4 % retention). TC reduces the aggregation of ZnV2O4 nanoparticles, allows abundant interaction with electrolyte, affords short ion diffusion pathways, serves as electrically conducting interconnects, and buffers the volume alterations thus imparting rapid kinetics and improved cycling stability. This performance is even better by the inclusion of a ZIF-8 metal-organic framework (MOF) layer at the separator, facing the cathode. ZIF-8 due to its nanoporous structure encompassing Zn−N based polyhedral clusters, efficiently confines Zn(II) ions at cathode during discharge and allows their facile diffusion through its open channels during charge thus maximizing Zn(II) ion storage capacity and reversibility and its highly crystalline robust structure also enhances the ZIB durability. This achievement is in line with the development of cost-effective, easily implementable non-aqueous ZIB that avoids the issues associated with aqueous electrolyte of limited potential stability window, corrosion of current collectors over time, and cell degradation and also offers long term stability and capacity. © 2021 Wiley-VCH Gmb
NUMERICAL SIMULATION OF FREE CONVECTION HEAT TRANSFER FROM A VERTICAL PLATE TO NON-NEWTONIAN NANOFLUIDS
No full textDirect numerical simulations of optimal thermal convection in rotating plane layer dynamos
No full textThe heat transfer behavior of convection-driven dynamos in a rotating plane
layer between two parallel plates, heated from below and cooled from the top,
is investigated. At a fixed rotation rate (Ekman Number, ) and fluid
properties (thermal and magnetic Prandtl numbers, ), both dynamo
convection (DC) and non-magnetic rotating convection (RC) simulations are
performed to demarcate the effect of magnetic field on heat transport at
different thermal forcings (Rayleigh Number,
). In this range, our turbulence
resolving simulations demonstrate the existence of an optimum thermal forcing,
at which heat transfer between the plates in DC exhibits maximum enhancement,
as compared to the heat transport in the RC simulations. Unlike any global
force balance reported in the literature, the present simulations reveal an
increase in the Lorentz force in the \textit{thermal boundary layer}, due to
stretching of magnetic field line by the vortices near the walls with no-slip
boundary condition. This increase in Lorentz force mitigates turbulence
suppression owing to the Coriolis force, resulting in enhanced turbulence and
heat transfe
Effects of kinematic and magnetic boundary conditions on the dynamics of convection-driven plane layer dynamos
No full textRapidly rotating convection-driven dynamos are investigated under different
kinematic and magnetic boundary conditions using DNS. At a fixed rotation rate,
represented by the Ekman number , the thermal forcing is
varied from 2 to 20 times its value at the onset of convection
(), keeping the fluid properties constant
(). The statistical behavior, force balance and heat transport
characteristics of the dynamos depend on boundary conditions that dictate both
boundary layer and the interior dynamics. At a fixed thermal forcing
(), the Ekman plumes in the presence of viscous boundary layers
lead to energetic vortices that result in higher enstrophy and kinetic helicity
with no-slip boundaries compared to free-slip boundaries. The structure and
strength of the magnetic field are also dictated by the boundary conditions.
Though the leading order force balance remains geostrophic, Lorentz force
dominates inside the thermal boundary layer with no-slip, electrically
conducting walls. Here, the Lorentz work term in the turbulent kinetic energy
budget is found to have components that exchange energy from the velocity field
to the magnetic field, and vice-versa. However, with no-slip, insulated walls,
all Lorentz work components perform unidirectional energy transfer to produce
magnetic energy from the kinetic energy of the fluid. The heat transfer
enhancement in dynamos, compared to non-magnetic rotating convection, exhibits
a peak in the range . For free-slip conditions, dynamo action
may alter the heat transport by suppressing the formation of large-scale
vortices. However, the highest heat transfer enhancement occurs when the
boundaries are no-slip, electrically conducting walls
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