In vivo NMR as a tool for probing molecular structure and dynamics in intact Chlamydomonas reinhardtii cells

We report the application of NMR dynamic spectral editing for probing the structure and dynamics of molecular constituents in fresh, intact cells and in freshly prepared thylakoid membranes of Chlamydomonas reinhardtii (Cr.) green algae. For isotope labeling, wild-type Cr. cells were grown on C-13 acetate-enriched minimal medium. 1D C-13 J-coupling based and dipolar-based MAS NMR spectra were applied to distinguish C-13 resonances of different molecular components. 1D spectra were recorded over a physiological temperature range, and whole-cell spectra were compared to those taken from thylakoid membranes, evaluating their composition and dynamics. A theoretical model for NMR polarization transfer was used to simulate the relative intensities of direct, J-coupling, and dipolar-based polarization from which the degree of lipid segmental order and rotational dynamics of the lipid acyl chains were estimated. We observe that thylakoid lipid signals dominate the lipid spectral profile of whole algae cells, demonstrating that with our novel method, thylakoid membrane characteristics can be detected with atomistic precision inside intact photosynthetic cells. The experimental procedure is rapid and applicable to fresh cell cultures, and could be used as an original approach for detecting chemical profiles, and molecular structure and dynamics of photosynthetic membranes in vivo in functional states.