Aix Marseille Univ, CNRS, LCB, Marseille, France.
Section of Microbiology and MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, SW72AZ, UK.
Sci Rep. 2018 Nov 26;8(1):17344. doi: 10.1038/s41598-018-35696-7.
Bacillus subtilis possesses four lipoteichoic acid synthases LtaS, YfnI, YvgJ and YqgS involved in the synthesis of cell wall. The crystal structure of the extracellular domain of LtaS revealed a phosphorylated threonine and YfnI was identified in two independent phosphoproteome studies. Here, we show that the four LTA synthases can be phosphorylated in vitro by the Ser/Thr kinase PrkC. Phosphorylation neither affects the export/release of YfnI nor its substrate binding. However, we observed that a phosphomimetic form of YfnI was active whereas its phosphoablative form was inactive. The phenotypes of the strains deleted for prkC or prpC (coding for a phosphatase) are fairly similar to those of the strains producing the phosphoablative or phosphomimetic YfnI proteins. Clear evidence proving that PrkC phosphorylates YfnI in vivo is still missing but our data suggest that the activity of all LTA synthases may be regulated by phosphorylation. Nonetheless, their function is non-redundant in cell. Indeed, the deletion of either ltaS or yfnI gene could restore a normal growth and shape to a ΔyvcK mutant strain but this was not the case for yvgJ or yqgS. The synthesis of cell wall must then be highly regulated to guarantee correct morphogenesis whatever the growth conditions.
枯草芽孢杆菌拥有四个参与细胞壁合成的脂磷壁酸合成酶 LtaS、YfnI、YvgJ 和 YqgS。LtaS 胞外结构域的晶体结构揭示了一个磷酸化的苏氨酸，并且在两项独立的磷酸化蛋白质组学研究中鉴定出 YfnI。在这里，我们表明四种 LTA 合成酶可以在体外被 Ser/Thr 激酶 PrkC 磷酸化。磷酸化既不影响 YfnI 的输出/释放，也不影响其底物结合。然而，我们观察到 YfnI 的磷酸模拟形式是有活性的，而其磷酸化失活形式是无活性的。prkC 或 prpC（编码磷酸酶）缺失的菌株的表型与产生磷酸化失活或磷酸模拟 YfnI 蛋白的菌株非常相似。仍然缺乏证明 PrkC 在体内磷酸化 YfnI 的明确证据，但我们的数据表明所有 LTA 合成酶的活性可能受到磷酸化的调节。尽管如此，它们的功能在细胞中并非冗余的。事实上，缺失 ltaS 或 yfnI 基因可以恢复 ΔyvcK 突变菌株的正常生长和形态，但对于 yvgJ 或 yqgS 则不然。因此，细胞壁的合成必须受到高度调控，以保证无论生长条件如何，正确的形态发生。
