Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA.
Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, Australia.
mBio. 2020 Sep 29;11(5):e02351-20. doi: 10.1128/mBio.02351-20.
The cholesterol-dependent cytolysins (CDCs) are bacterial, β-barrel, pore-forming toxins. A central enigma of the pore-forming mechanism is how completion of the prepore is sensed to initiate its conversion to the pore. We identified a motif that is conserved between the CDCs and a diverse family of nearly 300 uncharacterized proteins present in over 220 species that span at least 10 bacterial and 2 eukaryotic phyla. Except for this motif, these proteins exhibit little similarity to the CDCs at the primary structure level. Studies herein show this motif is a critical component of the sensor that initiates the prepore-to-pore transition in the CDCs. We further show by crystallography, single particle analysis, and biochemical studies of one of these CDC-like (CDCL) proteins from , a commensal of the malarial mosquito midgut, that a high degree of structural similarity exists between the CDC and CDCL monomer structures and both form large oligomeric pore complexes. Furthermore, the conserved motif in the CDCL crystal structure occupies a nearly identical position and makes similar contacts to those observed in the structure of the archetype CDC, perfringolysin O (PFO). This suggests a common function in the CDCs and CDCLs and may explain why only this motif is conserved in the CDCLs. Hence, these studies identify a critical component of the sensor involved in initiating the prepore-to-pore transition in the CDCs, which is conserved in a large and diverse group of distant relatives of the CDCs. The cholesterol-dependent cytolysins' pore-forming mechanism relies on the ability to sense the completion of the oligomeric prepore structure and initiate the insertion of the β-barrel pore from the assembled prepore structure. These studies show that a conserved motif is an important component of the sensor that triggers the prepore-to-pore transition and that it is conserved in a large family of previously unidentified CDC-like proteins, the genes for which are present in a vast array of microbial species that span most terrestrial environments, as well as most animal and human microbiomes. These studies establish the foundation for future investigations that will probe the contribution of this large family of CDC-like proteins to microbial survival and human disease.
胆固醇依赖性细胞溶素（CDCs）是细菌的β-桶状孔形成毒素。孔形成机制的一个核心难题是如何感知预孔的完成，从而启动其向孔的转化。我们鉴定了一个在 CDC 和一个由近 300 个未表征的蛋白组成的多样化家族之间保守的模体，这些蛋白存在于 220 多种物种中，跨越至少 10 个细菌和 2 个真核门。除了这个模体之外，这些蛋白在一级结构水平上与 CDC 的相似性很小。本文的研究表明，这个模体是一个关键的传感器组件，它启动了 CDC 中的预孔到孔的转变。我们进一步通过结晶学、单颗粒分析以及对一种来自 ，一种疟蚊中肠共生菌的 CDC 样（CDCL）蛋白的生化研究表明，CDC 和 CDCL 单体结构之间存在高度的结构相似性，并且两者都形成大的寡聚孔复合物。此外，在 CDCL 晶体结构中的保守模体占据了几乎相同的位置，并与在原型 CDC、产气荚膜梭菌溶素 O（PFO）的结构中观察到的结构相似，做出了相似的接触。这表明在 CDC 和 CDCL 中存在共同的功能，并且可能解释了为什么只有这个模体在 CDCL 中保守。因此，这些研究鉴定了参与启动 CDC 中预孔到孔的转变的传感器的一个关键组件，该组件在 CDC 的一个庞大而多样化的远亲群中保守。胆固醇依赖性细胞溶素的孔形成机制依赖于感知寡聚预孔结构完成的能力，并启动从组装的预孔结构中插入β-桶状孔。这些研究表明，一个保守的模体是触发预孔到孔的转变的传感器的一个重要组成部分，它在一个以前未被识别的 CDC 样蛋白的大家族中保守，这些基因存在于广泛的微生物物种中，这些物种跨越了大部分陆地环境，以及大多数动物和人类微生物组。这些研究为未来的研究奠定了基础，这些研究将探究这个庞大的 CDC 样蛋白家族对微生物生存和人类疾病的贡献。
