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 Elizabethkingia anophelis, 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 E. anophelis 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.

中文翻译：

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胆固醇依赖性溶细胞素的关键基序揭示了一大类相关蛋白

胆固醇依赖性溶细胞素（CDC）是细菌性的β桶状成孔毒素。孔形成机理的中心谜团是如何感测预孔的完成以启动其向孔的转化。我们确定了一个主题，它是CDC和不同家族的近300种未表征蛋白之间的保守分子，这些家族存在于220种以上的物种中，这些物种跨越至少10个细菌和2个真核生物门。除了该基序，这些蛋白质在一级结构水平上与CDC几乎没有相似性。本文的研究表明，该基序是传感器的重要组成部分，可启动CDC中的前孔到孔过渡。通过晶体学，单颗粒分析和生化研究，我们进一步显示了来自伊丽莎白女王的这些CDC样（CDCL）蛋白之一，这是疟疾蚊子中肠的代名词，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低聚孔复合体。此外，按蚊E. CDCL晶体结构中的保守基序占据几乎相同的位置，并与原型CDC，穿孔球菌溶血素O（PFO）结构中观察到的接触相似。这表明在CDC和CDCL中具有共同的功能，并且可以解释为什么在CDCL中仅保留该基序的原因。因此，这些研究确定了在CDC中涉及启动从孔前到孔的转变的传感器的重要组成部分，在CDC的许多远亲中，保守了这一点。