Cellular NMR

Conventional solution-phase NMR spectroscopy has been a powerful tool for looking at the structure of biological molecules. But it’s less useful for studying large complexes buried in cell membranes. Jan Tommassen, Marc Baldus, and coworkers at Utrecht University, in the Netherlands, now show that they can use solid-state NMR to study bacterial membrane proteins in isolated cell envelopes and in intact bacteria (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.1116478109). The cell envelope of gram-negative bacteria consists of inner and outer membranes separated by the peptidoglycan-containing periplasm. The researchers engineered Escherichia coli cells to produce an outer membrane protein called PagL and isotopically labeled the cells with ¹⁵N and ¹³C. They then collected two-dimensional correlation NMR spectra using pulse sequences tailored for solid-state NMR. They achieved similar spectral resolution whether PagL was synthetically reconstituted or in intact cellular envelopes. They also characterized other components of the cell envelope, including lipids, peptidoglycan, and lipoproteins. Cellular solid-state NMR should allow researchers to characterize biological processes mediated by complex protein molecular machines, the researchers note, “thereby bridging the gap between structural and cellular biology.”