Protein Unfolding During Anthrax Toxin Translocation

描述（由申请人提供）： 细菌病原体已经进化出一种通过毒素蛋白复合物感染宿主生物体的通用策略，该复合物模拟了AIB机制。活性的酶A部分与受体B部分结合;然后受体部分作为载体，将A部分从由膜双层分隔的隔离区室递送至细胞质。酶效应子通过其特定的催化活性使细胞的正常生理机能丧失。炭疽杆菌的三联毒素依赖于“分子注射器”B部分，即保护性抗原（PA），其在中性胞外pH下形成具有狭窄中心空腔的七肽环结构。两种不同的A部分效应物，致死因子（LF）和水肿因子（EF），结合PA七聚体。紧接着膜结合的PA/LF/EF复合物的内吞作用，内体酸化，触发PA七聚体的膜穿孔孔形式的同步形成，推测其将LF和EF注入胞质溶胶中。PA七聚体的狭窄中央腔太小，无法容纳完全天然的LF或EF，这可能是蛋白质解折叠减轻了易位。事实上，LF的稳定融合验证了这种类型的机制。各种荧光光谱和成像方法的现代进展，使蛋白质折叠途径的详细说明，即使在单分子水平。一个彻底的结构，精力充沛，和动力学的理解的事件序列导致和紧接其后的易位使用荧光方法将使改进的话语对潜在的治疗中毒，包括设计的蛋白质抑制剂和药物的设计和实施。

DESCRIPTION (provided by applicant): Bacterial pathogens have evolved a general strategy of infecting host organisms by means of toxin protein complexes that pattern the AIB mechanism. The active, enzymatic, A moiety binds the receptor, B moiety; the receptor moiety then acts as a vehicle that delivers the A moiety to the cytoplasm from an isolated compartment separated by a membrane bilayer. The enzymatic effector, by means of its specific catalytic activity, then disables the normal physiology of the cell. The tripartite toxin of Bacillus anthracis relies on a "molecular syringe" B moiety, Protective Antigen (PA), which forms a heptad ring structure with a narrow central cavity at neutral extracellular pH. Two different A moiety effectors, Lethal Factor (LF) and Edema Factor (EF), bind PA heptamer. Immediately following endocytosis of membrane bound PA/LF/EF complexes, endosomes acidify, triggering the synchronized formation of a membrane piercing pore form of PA heptamer that presumably injects LF and EF into the cytosol. The narrow central cavity of PA heptamer is too small to accommodate fully native LF or EF, invoking the possibility that translocation is mitigated by protein unfolding. Indeed, stabilized fusions of LF validate this type of mechanism. Modern advances in a variety of fluorescence spectroscopy and imaging methods have enabled the detailed elucidation of protein folding pathways even at the single molecule level. A thorough structural, energetic, and kinetic understanding of the sequence of events leading up to and immediately following translocation using fluorescence methods will enable improved discourse toward the design and implementation of potential therapies for intoxication, including designed protein inhibitors and drugs.