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Time-resolved electron holography and its application to an ionic liquid specimen.

ABSTRACT: Time-resolved electron holography was implemented in a transmission electron microscope by means of electron beam gating with a parallel-plate electrostatic deflector. Stroboscopic observations were performed by accumulating gated electron interference images while applying a periodic modulation voltage to a specimen. Electric polarization in an ionic liquid specimen was observed under applied fields. While a static electric field in the specimen was reduced by the polarization of the material, an applied field modulated at 10 kHz was not screened. This indicates that time-resolved electron holography is capable of determining the frequency limit of dynamic response of polarization in materials. Graphical Abstract.

SUBMITTER: Iwasaki Y

PROVIDER: S-EPMC10561666 | biostudies-literature | 2023 Oct

REPOSITORIES: biostudies-literature

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Time-resolved electron holography and its application to an ionic liquid specimen.

Iwasaki Yoh Y Akase Zentaro Z Shimada Keiko K Harada Ken K Shindo Daisuke D

Microscopy (Oxford, England) 20231001 5

Time-resolved electron holography was implemented in a transmission electron microscope by means of electron beam gating with a parallel-plate electrostatic deflector. Stroboscopic observations were performed by accumulating gated electron interference images while applying a periodic modulation voltage to a specimen. Electric polarization in an ionic liquid specimen was observed under applied fields. While a static electric field in the specimen was reduced by the polarization of the material, ...[more]

PMID: 36629509

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Project description:Eukaryotic cells exploit dynamic and compartmentalized ionic strength to impact a myriad of biological functions such as enzyme activities, protein-protein interactions, and catalytic functions. Herein, we investigated the fluorescence depolarization dynamics of recently developed ionic strength biosensors (mCerulean3-linker-mCitrine) in Hofmeister salt (KCl, NaCl, NaI, and Na2SO4) solutions. The mCerulean3-mCitrine acts as a Förster resonance energy transfer (FRET) pair, tethered together by two oppositely charged α-helices in the linker region. We developed a time-resolved fluorescence depolarization anisotropy approach for FRET analyses, in which the donor (mCerulean3) is excited by 425-nm laser pulses, followed by fluorescence depolarization analysis of the acceptor (mCitrine) in KE (lysine-glutamate), arginine-aspartate, and arginine-glutamate ionic strength sensors with variable amino acid sequences. Similar experiments were carried out on the cleaved sensors as well as an E6G2 construct, which has neutral α-helices in the linker region, as a control. Our results show distinct dynamics of the intact and cleaved sensors. Importantly, the FRET efficiency decreases and the donor-acceptor distance increases as the environmental ionic strength increases. Our chemical equilibrium analyses of the collapsed-to-stretched conformational state transition of KE reveal that the corresponding equilibrium constant and standard Gibbs free energy changes are ionic strength dependent. We also tested the existing theoretical models for FRET analyses using steady-state anisotropy, which reveal that the angle between the dipole moments of the donor and acceptor in the KE sensor are sensitive to the ionic strength. These results help establish the time-resolved depolarization dynamics of these genetically encoded donor-acceptor pairs as a quantitative means for FRET analysis, which complement traditional methods such as time-resolved fluorescence for future in vivo studies.

Dataset Information

Time-resolved electron holography and its application to an ionic liquid specimen.

Publications

Time-resolved electron holography and its application to an ionic liquid specimen.

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