Mycobacterium smegmatis MSMEG_0129 and Rv0164, its homologue in Mycobacterium tuberculosis, are single START-domain proteins essential for bacterial growth and survival, but their biochemical activities and biological roles remain undetermined. Here, we probed the possible functions of MSMEG_0129 and its underlying mechanisms by determining its cellular location, searching for its interaction partners and monitoring its transcription profile. MSMEG_0129, and Rv0164 by extension, were found to be cytosolic proteins rather than secreted components as previously understood. Increases in MSMEG_0129 expression at physiological levels accelerated bacterial growth in a proportional manner, but additional growth acceleration was not observed when MSMEG_0129 was overexpressed up to 20 fold. MSMEG_0129 is a short-lived protein, unstable at both the mRNA and protein levels. Co-IP and GST pull-down assays showed that MSMEG_0129 interacts with the ClpP2 protease and a global transcription factor, CarD, their expression being correlated with that of MSMEG_0129. Nutrient deficiency led to the downregulation of MSMEG_0129 but upregulation of CarD. However, in the context of constitutive MSMEG_0129 overexpression under nutrient-rich or starvation conditions, the mRNA level of CarD was reduced 3 fold. Conversely, expression of ClpP2 decreased with MSMEG_0129 downregulation under starvation conditions, but increased 4–8 fold when MSMEG_0129 was overexpressed. Our data suggest that MSMEG_0129, and Rv0164 by analogy, are likely to be nutrition sensing factors that regulate mycobacterial growth and may be involved in signal transfer under nutrient deficiency, possibly via physical and regulatory interactions with CarD and ClpP2.

耻垢分枝杆菌MSMEG_0129和Rv0164，其在结核分枝杆菌中的同系物是对细菌生长和存活必不可少的单个START结构域蛋白，但其生化活性和生物学作用仍未确定。在这里，我们通过确定MSMEG_0129的细胞位置，搜索其相互作用伴侣并监测其转录谱，探讨了MSMEG_0129的可能功能及其潜在机制。MSMEG_0129和Rv0164通过扩展被发现是胞质蛋白，而不是先前理解的分泌成分。在生理水平上MSMEG_0129表达的增加按比例加快了细菌的生长，但是当MSMEG_0129过度表达达20倍时，未观察到额外的生长加速。MSMEG_0129是一种短暂的蛋白质，在mRNA和蛋白质水平上均不稳定。Co-IP和GST下拉分析表明MSMEG_0129与ClpP2蛋白酶和全局转录因子CarD相互作用，它们的表达与MSMEG_0129的表达相关。营养不足导致MSMEG_0129的下调，但CarD的上调。但是，在营养丰富或饥饿条件下本构性MSMEG_0129过表达的情况下，CarD的mRNA水平降低了3倍。相反，在饥饿条件下，ClpP2的表达随MSMEG_0129的下调而降低，但当MSMEG_0129过表达时，ClpP2的表达增加4-8倍。我们的数据表明，MSMEG_0129和Rv0164类似地可能是调节分枝杆菌生长的营养敏感因子，并可能在营养缺乏时参与信号传递，