Department of Chemistry & Biochemistry, University of Massachusetts Dartmouth, North Dartmouth, MA, 02747, USA.
Botulinum Research Center, Institute of Advanced Sciences, North Dartmouth, MA, 02747, USA.
Sci Rep. 2018 Jun 11;8(1):8884. doi: 10.1038/s41598-018-26764-z.
Botulinum neurotoxin (BoNT) is responsible for botulism, a clinical condition resulting in flaccid muscle paralysis and potentially death. The light chain is responsible for its intracellular toxicity through its endopeptidase activity. Available crystal structures of BoNT/A light chains (LCA) are based on various truncated versions (tLCA) of the full-length LCA (fLCA) and do not necessarily reflect the true structure of LCA in solution. The understanding of the mechanism of action, longevity of intoxication, and an improved development of endopeptidase inhibitors are dependent on first having a better insight into the structure of LCA in solution. Using an array of biophysical techniques, we report that the fLCA structure is significantly more flexible than tLCA in solution, which may be responsible for its dramatically higher enzymatic activity. This seems to be achieved by a much stronger, more rapid binding to substrate (SNAP-25) of the fLCA compared to tLCA. These results suggest that the C-terminus of LCA plays a critical role in introducing a flexible structure, which is essential for its biological function. This is the first report of such a massive structural role of the C-terminus of a protein being critical for maintaining a functional state.
肉毒杆菌神经毒素（BoNT）是肉毒中毒的致病因子，可导致肌肉瘫痪，并可能致人死亡。轻链通过其内切酶活性发挥其细胞内毒性。已有的 BoNT/A 轻链（LCA）晶体结构基于全长 LCA（fLCA）的各种截断版本（tLCA），不一定反映 LCA 在溶液中的真实结构。对作用机制、中毒持续时间的理解，以及内肽酶抑制剂的改进开发，都依赖于首先更好地了解 LCA 在溶液中的结构。本研究使用一系列生物物理技术，报告称 fLCA 在溶液中的结构比 tLCA 显著更具灵活性，这可能是其酶活性显著提高的原因。这似乎是通过与 tLCA 相比，fLCA 与底物（SNAP-25）更强、更快的结合来实现的。这些结果表明，LCA 的 C 末端在引入灵活的结构中起着关键作用，这对于其生物学功能至关重要。这是第一个报道蛋白质 C 末端的这种大规模结构作用对于维持功能状态至关重要的报告。
