Variations in TcdB activity and the hypervirulence of emerging strains of Clostridium difficile.
Variations in TcdB activity and the hypervirulence of emerging strains of Clostridium difficile.
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DOI：
10.1371/journal.ppat.1001061
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发表时间：
2010-08-19
期刊：
影响因子：
6.7
通讯作者：
Ballard JD
中科院分区：
文献类型：
--
作者：
Lanis JM;Barua S;Ballard JD
过去十年中出现了艰难梭菌的高毒力菌株，增加了被这种机会性病原体感染的患者的发病率和死亡率。最近的研究表明，来自高毒力菌株 (TcdBHV) 的主要艰难梭菌毒力因子 TcdB 在体外比来自历史菌株 (TcdBHIST) 的 TcdB 更具细胞毒性。目前的研究调查了 TcdB 向性改变的体内影响，以及导致这种毒素的两种形式之间活性差异的潜在机制。蛋白质序列分析、使用斑马鱼模型系统的体内研究以及细胞进入与荧光测定相结合的组合被用来定义 TcdBHV 和 TcdBHIST 之间的关键差异。序列分析发现，TcdB 是艰难梭菌致病位点表达的变异最大的蛋白质。与这些序列差异一致，发现 TcdBHV 的体内作用比 TcdBHIST 引起的作用更广泛、更明显。 TcdBHV 毒性的增加与该毒素比 TcdBHIST 更快、更早地进入细胞内吞作用的能力有关。实验确定了更快进入细胞的潜在生化机制，证明 TcdBHV 在比 TcdBHIST 高得多的 pH 值下会经历酸诱导的构象变化。已知这种与 pH 相关的构象变化是 TcdB 膜插入和易位的激发步骤。这些数据提供了对 TcdB 活性的关键变化的深入了解，这种变化导致了艰难梭菌的高毒力的出现。 艰难梭菌是一种产孢细菌，会污染医院并感染接受抗生素治疗的患者。目前，艰难梭菌是发达国家医院获得性腹泻的主要原因。最令人担忧的是，由于艰难梭菌病原体的高毒力菌株的出现，最近艰难梭菌患者的死亡率有所增加。目前的研究结果表明，疾病严重程度的这种变化可能是由于新菌株产生了艰难梭菌主要毒力因子 TcdB 的变体形式。研究结果表明，来自高毒力菌株的 TcdB 在体内靶向范围更广的细胞，并且能够比来自艰难梭菌历史菌株的 TcdB 更快地转位到靶细胞中。来自高毒力艰难梭菌的 TcdB 进入细胞的速度更快，这似乎是由于该毒素能够在比历史菌株的 TcdB 更高的 pH 值下进行膜易位所需的构象变化。迄今为止，人们对新出现的艰难梭菌菌株毒力增加的根本原因知之甚少。这些发现提供了对该问题的深入了解，并表明 TcdB 活性的变化可能是艰难梭菌新兴菌株超毒力的一个重要因素。
Hypervirulent strains of Clostridium difficile have emerged over the past decade, increasing the morbidity and mortality of patients infected by this opportunistic pathogen. Recent work suggested the major C. difficile virulence factor, TcdB, from hypervirulent strains (TcdBHV) was more cytotoxic in vitro than TcdB from historical strains (TcdBHIST). The current study investigated the in vivo impact of altered TcdB tropism, and the underlying mechanism responsible for the differences in activity between the two forms of this toxin. A combination of protein sequence analyses, in vivo studies using a Danio rerio model system, and cell entry combined with fluorescence assays were used to define the critical differences between TcdBHV and TcdBHIST. Sequence analysis found that TcdB was the most variable protein expressed from the pathogenicity locus of C. difficile. In line with these sequence differences, the in vivo effects of TcdBHV were found to be substantially broader and more pronounced than those caused by TcdBHIST. The increased toxicity of TcdBHV was related to the toxin's ability to enter cells more rapidly and at an earlier stage in endocytosis than TcdBHIST. The underlying biochemical mechanism for more rapid cell entry was identified in experiments demonstrating that TcdBHV undergoes acid-induced conformational changes at a pH much higher than that of TcdBHIST. Such pH-related conformational changes are known to be the inciting step in membrane insertion and translocation for TcdB. These data provide insight into a critical change in TcdB activity that contributes to the emerging hypervirulence of C. difficile. Clostridium difficile is a spore-forming bacterium that contaminates hospitals and infects patients undergoing antibiotic therapy. C. difficile is now the leading cause of hospital-acquired diarrhea in developed countries. Most concerning has been the recent increase in mortality of C. difficile patients due to the emergence of a hypervirulent strain of this pathogen. Results from the current study suggest this change in disease severity may be due to new strains producing a variant form of C. difficile's major virulence factor, TcdB. The findings indicate TcdB from hypervirulent strains targets a much broader range of cells in vivo and is able to translocate into target cells more quickly than TcdB from historical strains of C. difficile. The more rapid cell entry by TcdB from hypervirulent C. difficile appears to be due to the toxin's capacity to undergo conformational changes necessary for membrane translocation at a higher pH than TcdB from historical strains. To date, very little has been learned about the underlying reasons for the increased virulence of emerging C. difficile strains. These findings provide insight into this problem and suggest variations in TcdB activity could be an important contributing factor to the hypervirulence of emerging strains of C. difficile.
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影响因子：
6.4
作者：
Geric, B;Carman, RJ;Johnson, S
通讯作者：
Johnson, S
DOI：
10.1073/pnas.93.22.12531
发表时间：
1996-10-29
影响因子：
11.1
作者：
Ballard, JD;Collier, RJ;Starnbach, MN
通讯作者：
Starnbach, MN
影响因子：
4.8
作者：
Busch, C;Hofmann, F;Aktories, K
通讯作者：
Aktories, K
DOI：
10.1073/pnas.0604725103
发表时间：
2006-09-19
影响因子：
11.1
作者：
Hamm, Elaine E.;Voth, Daniel E.;Ballard, Jimmy D.
通讯作者：
Ballard, Jimmy D.
影响因子：
64.8
作者：
JUST, I;SELZER, J;AKTORIES, K
通讯作者：
AKTORIES, K