Spectral-Density Mapping of 13Calpha-1Halpha Vector Dynamics Using Dipolar Relaxation Rates Measured at Several...

Area of Science:

• Biophysics
• Structural Biology
• Nuclear Magnetic Resonance (NMR) Spectroscopy

Background:

• Spectral-density mapping is crucial for characterizing molecular dynamics.
• Previous studies on motilin used limited magnetic fields, affecting accuracy.
• Carbon-proton (13C-1H) vectors are ideal for this technique due to dominant dipolar interactions.

Purpose of the Study:

• To improve the accuracy of spectral-density function J(omega) calculations for motilin.
• To extend the frequency sampling range of spectral-density mapping up to 750 MHz.
• To refine the understanding of molecular motion in peptide hormones.

Main Methods:

• Extended spectral-density mapping of a 13Calpha-1Halpha vector in motilin across three polarizing fields (9.4, 11.7, 14.1 T).
• Transformed time-domain relaxation rates into the frequency domain using spectral-density mapping.
• Applied error weighting for fitting dynamic models to spectral density points.

Main Results:

• Achieved improved accuracy in spectral-density function J(omega) and extended sampling range.
• Eliminated large relative errors in J(omegaH) by utilizing J(omegaH - omegaC) and J(omegaH + omegaC) from different fields.
• Found the influence of J(omegaH) on the high-frequency spectral-density function to be negligible.

Conclusions:

• The high-frequency spectral-density function is primarily determined by factors other than transverse relaxation rates.
• Model-free analysis with adjustable internuclear distance provided a reasonable fit for J(0) and J(omegaC) points.
• The high-frequency slope of the spectral-density function, defined by J(omegaH - omegaC) and J(omegaH + omegaC), could not be fully reproduced, indicating limitations in current models.