Nanometric distance measurements between Mn(ii)DOTA centers

Area of Science:

• Biophysics
• Structural Biology
• Magnetic Resonance Spectroscopy

Background:

• Pulse electron-electron double resonance (PELDOR) is a powerful technique for determining distances in biological macromolecules.
• Manganese(II) (Mn(ii)) ions are of interest for high-field/frequency applications, but their use in PELDOR is underexplored.

Purpose of the Study:

• To investigate Mn(ii)-Mn(ii) PELDOR distance measurements using Mn(ii)DOTA spin labels.
• To assess the suitability of Mn(ii)DOTA for high-field PELDOR applications in biological systems.

Main Methods:

• High-field (94 GHz) PELDOR measurements on polyproline II (PPII) helices doubly spin-labeled with Mn(ii)DOTA.
• Analysis of Mn-Mn distances and distance distribution profiles.
• Spin-Hamiltonian calculations to interpret spectral features.

Main Results:

• Accurate Mn-Mn distances and distribution profiles were obtained for PPII helices, matching molecular models.
• Additional spectral features were observed, attributed to the pseudo-secular component of the dipolar interaction.
• The pseudo-secular component's influence on distance distributions was found to be limited.

Conclusions:

• Mn(ii)DOTA spin labels are suitable for high-field PELDOR distance measurements.
• This technique has potential for studying proteins and other biological systems.
• Understanding dipolar interaction components is crucial for accurate PELDOR analysis.