Zhou Donghua H, Shah Gautam, Cormos Mircea, Mullen Charles, Sandoz Dennis, Rienstra Chad M
Department of Chemistry, Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
J Am Chem Soc. 2007 Sep 26;129(38):11791-801. doi: 10.1021/ja073462m. Epub 2007 Aug 29.
Remarkable progress in solid-state NMR has enabled complete structure determination of uniformly labeled proteins in the size range of 5-10 kDa. Expanding these applications to larger or mass-limited systems requires further improvements in spectral sensitivity, for which inverse detection of 13C and 15N signals with 1H is one promising approach. Proton detection has previously been demonstrated to offer sensitivity benefits in the limit of sparse protonation or with approximately 30 kHz magic-angle spinning (MAS). Here we focus on experimental schemes for proteins with approximately 100% protonation. Full protonation simplifies sample preparation and permits more complete chemical shift information to be obtained from a single sample. We demonstrate experimental schemes using the fully protonated, uniformly 13C,15N-labeled protein GB1 at 40 kHz MAS rate with 1.6-mm rotors. At 500 MHz proton frequency, 1-ppm proton line widths were observed (500 +/- 150 Hz), and the sensitivity was enhanced by 3 and 4 times, respectively, versus direct 13C and 15N detection. The enhanced sensitivity enabled a family of 3D experiments for spectral assignment to be performed in a time-efficient manner with less than a micromole of protein. CANH, CONH, and NCAH 3D spectra provided sufficient resolution and sensitivity to make full backbone and partial side-chain proton assignments. At 750 MHz proton frequency and 40 kHz MAS rate, proton line widths improve further in an absolute sense (360 +/- 115 Hz). Sensitivity and resolution increase in a better than linear manner with increasing magnetic field, resulting in 14 times greater sensitivity for 1H detection relative to that of 15N detection.
固态核磁共振技术取得的显著进展,已能够确定分子量在5至10 kDa范围内的均匀标记蛋白质的完整结构。要将这些应用扩展到更大或受质量限制的系统,需要进一步提高光谱灵敏度,其中利用1H对13C和15N信号进行反向检测是一种很有前景的方法。此前已证明,在质子化稀疏或约30 kHz魔角旋转(MAS)的极限情况下,质子检测具有灵敏度优势。在这里,我们关注的是质子化率约为100%的蛋白质的实验方案。完全质子化简化了样品制备,并能从单个样品中获得更完整的化学位移信息。我们展示了使用完全质子化、均匀13C、15N标记的蛋白质GB1,在40 kHz MAS速率和1.6毫米转子条件下的实验方案。在500 MHz质子频率下,观察到质子线宽为1 ppm(500±150 Hz),与直接13C和15N检测相比,灵敏度分别提高了3倍和4倍。灵敏度的提高使得能够以高效的方式,用不到一微摩尔的蛋白质进行一系列用于光谱归属的三维实验。CANH、CONH和NCAH三维光谱提供了足够的分辨率和灵敏度,以实现完整的主链和部分侧链质子归属。在750 MHz质子频率和40 kHz MAS速率下,质子线宽在绝对值上进一步改善(360±115 Hz)。随着磁场强度的增加,灵敏度和分辨率以优于线性的方式增加,导致1H检测的灵敏度相对于15N检测提高了14倍。