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Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
Published on: September 17, 2017
Three-dimensional solid-state NMR study of a seven-helical integral membrane proton pump--structural insights
Lichi Shi1, Mumdooh A M Ahmed, Wurong Zhang
1Department of Physics, University of Guelph, 50 Stone Road East, Guelph, Ontario, Canada N1G 2W1.
Journal of Molecular Biology
|February 27, 2009
Summary
Proteorhodopsin (PR), a light-driven proton pump found in bacteria, has had its structure investigated using NMR spectroscopy. This study reveals key structural details of PR, including helix distortions and protonation states.
Area of Science:
- Biochemistry
- Structural Biology
- Microbiology
Background:
- Proteorhodopsin (PR) is a ubiquitous, light-driven proton pump found in diverse bacteria.
- Its seven-transmembrane alpha-helical structure presents challenges for traditional structural studies.
- The widespread distribution suggests a significant photobiological role.
Purpose of the Study:
- To elucidate the three-dimensional structure of proteorhodopsin.
- To gain insights into the protonation states and secondary structure elements of PR.
- To provide a structural basis for understanding PR's function.
Main Methods:
- Magic-angle spinning (MAS) NMR spectroscopy on lipid-reconstituted PR.
- Three-dimensional chemical shift correlation experiments with reverse labeling.
- Sequential assignment of 13C and 15N backbone and side-chain chemical shifts.
Main Results:
- Well-resolved NMR spectra were obtained for lipid-reconstituted PR.
- Sequential assignments were achieved for 103 residues.
- Protonation states of key carboxylic acids (Asp227 ionized, Glu142 neutral) were confirmed.
- Boundaries and distortions of transmembrane alpha-helices were identified.
- Secondary structure elements in loops and helical kinks were detected.
Conclusions:
- NMR spectroscopy is effective for studying proteorhodopsin structure.
- Structural insights include helix distortions, loop structures, and specific residue protonation.
- The findings support similarities to bacteriorhodopsin's structure, including proline and non-proline kinks.
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