# Gd(III)-Gd(III) RIDME for In-Cell EPR Distance Determination

## TL;DR

This paper demonstrates that RIDME, a pulsed EPR technique, can effectively determine biomolecular distances inside cells, offering advantages over existing methods like DEER.

## Contribution

The study introduces in-cell RIDME as a new method for in vivo distance measurements, showing its improved performance over DEER in cellular environments.

## Key findings

- RIDME provides larger modulation depth than DEER in cells.
- RIDME does not exhibit artificial broadening in distance distributions.
- RIDME's overtone coefficients are consistent inside cells and in solution.

## Abstract

In-cell distance determination by EPR reveals essential structural information about biomacromolecules under native conditions. We demonstrate that the pulsed EPR technique RIDME (relaxation induced dipolar modulation enhancement) can be utilized for such distance determination. The performance of in-cell RIDME has been assessed at Q band using stiff molecular rulers labelled with Gd(III)-PyMTA tags and microinjected into X. laevis oocytes. The overtone coefficients are determined to be the same for protonated aqueous solutions and inside cells. As compared to in-cell DEER (double electron-electron resonance, also abbreviated as PELDOR), in-cell RIDME features approximately 5 times larger modulation depth and does not show artificial broadening in the distance distributions due to the effect of pseudo-secular terms.

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Source: https://tomesphere.com/paper/1902.01254