Partial ¹³C and ¹⁵N chemical-shift assignments of the disulfide-bond-forming enzyme DsbB by 3D magic-angle spinning NMR spectroscopy

DsbB is a 20 kDa Escherichia coli inner-membrane protein that catalyzes disulfide-bond formation in periplasmic proteins. We report highly resolved, multidimensional magic-angle spinning NMR spectra at 750 MHz ¹H frequency, which enable partial ¹³C and ¹⁵N chemical-shift assignments of the signals. The narrow line widths observed indicate excellent microscopic order of the protein sample, suitable for full structure determination by solid-state NMR. Experiments were performed exclusively on uniformly ¹³C,¹⁵N-labeled DsbB. Chemical-shift-correlation experiments based on dipolar transfer yielded strong signals in the 3D spectra, many of which have been site-specifically assigned to the four transmembrane helices of DsbB. Significant numbers of additional residues have been assigned to stretches of amino acids, although not yet placed in the amino acid sequence. We also report the temperature dependence of signal intensities from -50°C to 0°C, a range over which samples of DsbB are highly stable. Structural and dynamic information derived from SSNMR studies can give insight into DsbB in a state that so far has not been successfully crystallized.