Tag Archives: cell biology

Nanoscale dipole dynamics of protein membranes studied by broadband dielectric microscopy

The dielectric permittivity of membranes is important for many fundamental electrophysiological functions like selective transport in ion channels, action potential propagation and energy generation.*

In their article “Nanoscale dipole dynamics of protein membranes studied by broadband dielectric microscopy” George Gramse, Andreas Schönhals and Ferry Kienberger investigate the nearfield dipole mobility of protein membranes in a wide frequency range from 3 kHz to 10 GHz.*

They achieved their results by adding the frequency as a second fundamental dimension to quantitative dielectric microscopy thereby demonstrating the possibilities of broadband dielectric microscopy for the investigation of dynamic processes in cell bioelectricity at the individual molecular level. Furthermore, the technique may also shed light on local dynamic processes in related materials science applications like semiconductor research or nano-electronics.*

All AFM measurements were carried out at 25 °C using a NANOSENSORS Platinum Silicide AFM probe ( PtSi-FM ).

Fig. 2 from “Nanoscale dipole dynamics of protein membranes studied by broadband dielectric microscopy” by Gramse et al.: image a) shows the AFM topography and image b) shows the corresponding C′′(z)/C′′dry(z) image obtained in lift mode at z = 10 nm above the last scan line and at a frequency of ω = 10 kHz (inset at 1 MHz). The corresponding topography and C′′(z)/C′′dry(z) profile lines are shown in  image c). Solid lines correspond to profile lines at 10 kHz and the dashed line to 1 MHz. Image d) shows the normalized dielectric spectra on the substrate and protein membrane at constant height z′ = 15 nm and lift mode z = 15 nm. Black solid lines represent fitting with eqn (1) and (2). image e) shows the resulting complex dielectric functions ε′r(f) and ε′′r(f)2 (using the relation ε′′r(f) = −(π/2∂)ε′r/∂ln(2πf)38). All measurements are carried out at 25 °C using conductive and wear-resistant Platinum Silicide AFM probes  (PtSi-FM ) from NANOSENSORS (Germany). Humidity was changed and left to stabilize for 2–3 hours. Imaging conditions were adjusted to maintain the lift distance for the dielectric images identical.

Fig. 2 from “Nanoscale dipole dynamics of protein membranes studied by broadband dielectric microscopy” by Gramse et al.: (a) AFM topography and (b) corresponding C′′(z)/C′′dry(z) image obtained in lift mode at z = 10 nm above the last scan line and at a frequency of ω = 10 kHz (inset at 1 MHz). The corresponding topography and C′′(z)/C′′dry(z) profile lines are shown in (c). Solid lines correspond to profile lines at 10 kHz and the dashed line to 1 MHz. (d) Normalized dielectric spectra on the substrate and protein membrane at constant height z′ = 15 nm and lift mode z = 15 nm. Black solid lines represent fitting with eqn (1) and (2). (e). Resulting complex dielectric functions ε′r(f) and ε′′r(f)2 (using the relation ε′′r(f) = −(π/2∂)ε′r/∂ln(2πf)38).
All measurements are carried out at 25 °C using PtSi-FM tips from NANOSENSORS (Germany). Humidity was changed and left to stabilize for 2–3 hours. Imaging conditions were adjusted to maintain the lift distance for the dielectric images identical.

*Georg Gramse, Andreas Schönhals, Ferry Kienberger
Nanoscale dipole dynamics of protein membranes studied by broadband dielectric microscopy
Nanoscale, 2019, 11, 4303-4309
DOI: 10.1039/C8NR05880F

Please follow this external link for the full article: https://pubs.rsc.org/en/content/articlehtml/2019/nr/c8nr05880f

Open Access The article “Nanoscale dipole dynamics of protein membranes studied by broadband dielectric microscopy” by George Gramse, Andreas Schönhals and Ferry Kienberger is licensed under a Creative Commons Attribution 3.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. To view a copy of this license, visit https://creativecommons.org/licenses/by/3.0/

Cdk1-mediated DIAPH1 phosphorylation maintains metaphase cortical tension and inactivates the spindle assembly checkpoint at anaphase

“Animal cells undergo rapid rounding during mitosis, ensuring proper chromosome segregation, during which an outward rounding force abruptly increases upon prometaphase entry and is maintained at a constant level during metaphase. Initial cortical tension is generated by the actomyosin system to which both myosin motors and actin network architecture contribute. However, how cortical tension is maintained and its physiological significance remain unknown.”*

In their publication “Cdk1-mediated DIAPH1 phosphorylation maintains metaphase cortical tension and inactivates the spindle assembly checkpoint at anaphase” Koutarou Nishimura et al. describe the uncovering of a previously unknown mechanism by which Cdk1 coordinates cortical tension maintenance and SAC inactivation at anaphase onset.*

For the AFM force measurements described in this publication NANOSENSORS™ TL-CONT tipless AFM cantilevers were used. The spring constant of individual cantilevers was determined by a thermal method.

NANOSENSORS™ tipless cantilever for various applications in atomic force microscopy and force measurements
NANOSENSORS™ tipless cantilever

*Koutarou Nishimura, Yoshikazu Johmura, Katashi Deguchi, Zixian Jiang, Kazuhiko S. K. Uchida, Narumi Suzuki, Midori Shimada, Yoshie Chiba, Toru Hirota, Shige H. Yoshimura, Keiko Kono & Makoto Nakanishi
Cdk1-mediated DIAPH1 phosphorylation maintains metaphase cortical tension and inactivates the spindle assembly checkpoint at anaphase
Nature Communications, volume 10, Article number: 981 (2019)
DOI: https://doi.org/10.1038/s41467-019-08957-w

Please follow this external link to the full article: https://www.nature.com/articles/s41467-019-08957-w

Open Access The article “Cdk1-mediated DIAPH1 phosphorylation maintains metaphase cortical tension and inactivates the spindle assembly checkpoint at anaphase” by Koutarou Nishimura et al. is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.