Backbone dynamics of bacteriorhodopsin as studied by (13)C solid-state NMR spectroscopy

Area of Science:

• Biophysics
• Structural Biology
• Solid-state NMR Spectroscopy

Background:

• Bacteriorhodopsin is a light-driven proton pump crucial for cellular energy.
• Understanding protein dynamics is key to elucidating its function.
• Site-specific labeling allows for detailed motional analysis.

Purpose of the Study:

• To investigate the surface dynamics of bacteriorhodopsin using site-specific labeling.
• To quantify motional amplitudes and frequencies of amino acid residues.
• To correlate protein dynamics with structural elements.

Main Methods:

• Utilized [3-(13)C]Alanine-labeled bacteriorhodopsin.
• Employed two-dimensional dipolar and chemical shift (DIPSHIFT) correlation spectroscopy.
• Measured site-specific (13)C-(1)H dipolar couplings in solid-state NMR.

Main Results:

• Identified motional averaging of alanine Calpha-Cbeta vectors beyond methyl group rotation.
• Determined molecular order parameters between 0.25 and 0.29 for mobile sites.
• Localized dynamic regions to specific loops and helices, including Ala103, Ala235, Ala196, Ala228, Ala233, and Ala51.
• Observed signal loss for Ala160 in the E-F loop, suggesting significant dynamics.

Conclusions:

• Provided direct evidence for fluctuation motions of alanine Calpha-Cbeta vectors in wild-type bacteriorhodopsin.
• Demonstrated that protein surface dynamics are significant at ambient temperatures.
• Highlighted the utility of solid-state NMR for characterizing protein motion in complex biological systems.