Gd(III)-Gd(III) Relaxation-Induced Dipolar Modulation Enhancement for In-Cell Electron Paramagnetic Resonance Distance Determination.

Mykhailo Azarkh,Adelheid Godt,Maxim Yulikov,Jörg W A Fischer,Malte Drescher,Mian Qi,Anna Bieber

doi:10.1021/acs.jpclett.9b00340

Abstract

In-cell distance determination by electron paramagnetic resonance (EPR) spectroscopy 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 labeled with Gd(III)-PyMTA and microinjected into Xenopus 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 pseudosecular terms.

Highlights

In-cell distance determination by electron paramagnetic resonance (EPR) spectroscopy reveals essential structural information about biomacromolecules under native conditions
We demonstrate that the pulsed EPR technique RIDME can be utilized for such distance determination
By combination of pulsed EPR techniques with site-directed spin labeling, distances in the range up to 8 nm, and under the very special condition of a perdeuterated biomacromolecule up to 16 nm, can be determined.[1−10] Distance determination is based on the measurement of the dipolar coupling frequency, ωdd, which is inversely proportional to the cube of the distance between two magnetically coupled spins and can be performed in any kind of environment, including living cells