Bacterial dormancy can take many forms, including formation of Bacillus endospores, Streptomyces exospores, and metabolically latent Mycobacterium cells. In the actinobacteria, including the streptomycetes and mycobacteria, the rapid resuscitation from a dormant state requires the activities of a family of cell-wall lytic enzymes called resuscitation-promoting factors (Rpfs). Whether Rpf activity promotes resuscitation by generating peptidoglycan fragments (muropeptides) that function as signaling molecules for spore germination or by simply remodeling the dormant cell wall has been the subject of much debate. Here, to address this question, we used mutagenesis and peptidoglycan binding and cleavage assays to first gain broader insight into the biochemical function of diverse Rpf enzymes. We show that their LysM and LytM domains enhance Rpf enzyme activity; their LytM domain and, in some cases their LysM domain, also promoted peptidoglycan binding. We further demonstrate that the Rpfs function as endo-acting lytic transglycosylases, cleaving within the peptidoglycan backbone. We also found that unlike in other systems, Rpf activity in the streptomycetes is not correlated with peptidoglycan-responsive Ser/Thr kinases for cell signaling, and the germination of rpf mutant strains could not be stimulated by the addition of known germinants. Collectively, these results suggest that in Streptomyces, Rpfs have a structural rather than signaling function during spore germination, and that in the actinobacteria, any signaling function associated with spore resuscitation requires the activity of additional yet to be identified enzymes.

中文翻译：

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LysM 和 LytM 结构域在复苏促进因子 (Rpf) 活性和 Rpf 介导的肽聚糖裂解和休眠孢子重新激活中的作用。

细菌休眠可以采取多种形式，包括芽孢杆菌内生孢子、链霉菌外生孢子和代谢潜伏分枝杆菌细胞的形成。在放线菌中，包括链霉菌和分枝杆菌，从休眠状态快速复苏需要细胞壁裂解酶家族的活性，称为复苏促进因子（Rpfs）。Rpf 活性是否通过产生作为孢子萌发信号分子的肽聚糖片段（壁肽）或通过简单地重塑休眠细胞壁来促进复苏，一直是很多争论的主题。在这里，为了解决这个问题，我们使用诱变和肽聚糖结合和裂解测定，首先更广泛地了解各种 Rpf 酶的生化功能。我们发现它们的 LysM 和 LytM 结构域增强了 Rpf 酶的活性；它们的 LytM 结构域，在某些情况下它们的 LysM 结构域，也促进肽聚糖结合。我们进一步证明 Rpfs 作为内切作用裂解转糖基酶发挥作用，在肽聚糖主链内裂解。我们还发现，与其他系统不同，链霉菌中的 Rpf 活性与细胞信号转导的肽聚糖响应性 Ser/Thr 激酶不相关，并且添加已知萌芽体无法刺激 rpf 突变株的萌发。总的来说，这些结果表明，在链霉菌中，Rpfs 在孢子萌发过程中具有结构功能而不是信号功能，而在放线菌中，任何与孢子复苏相关的信号功能都需要其他尚未鉴定的酶的活性。