The United Graduate School of Agricultural Sciences, Iwate University, Morioka, Iwate, Japan.
The United Graduate School of Agricultural Sciences, Iwate University, Morioka, Iwate, Japan; Department of Biological Chemistry and Food Sciences, Faculty of Agriculture, Iwate University, Morioka, Iwate, Japan.
Biochem Biophys Res Commun. 2019 Mar 19;510(4):636-642. doi: 10.1016/j.bbrc.2019.01.145. Epub 2019 Feb 8.
MPIase is a glycolipid involved in protein integration in E. coli. Recently, we identified CdsA, a CDP-diacylglycerol (CDP-DAG) synthase, as a biosynthetic enzyme for MPIase. YnbB is a CdsA paralogue with a highly homologous C-terminal half. Under CdsA-depleted conditions, YnbB overproduction restored MPIase expression, but not phospholipid biosynthesis. YnbB complemented the growth defect of the cdsA knockout when Tam41p, a mitochondrial CDP-DAG synthase, was co-expressed, suggesting that YnbB possesses sufficient activity for MPIase biosynthesis, but not for phospholipid biosynthesis. Consistently, a chimera consisting of the CdsA N-terminal half and the YnbB C-terminal half (CdsA-N-YnbB-C) complemented the cdsA knockout by itself, but a chimera consisting of the YnbB N-terminal half and the CdsA C-terminal half (YnbB-N-CdsA-C) required co-expression of Tam41p for the complementation. The biosynthetic rate for CDP-DAG in CdsA and CdsA-N-YnbB-C was much faster than that in YnbB and YnbB-N-CdsA-C, indicating that the N-terminal half of CdsA accelerates CDP-DAG biosynthesis to give the fast cell growth. Therefore, the role of YnbB seems to be as a backup for MPIase biosynthesis, suggesting that YnbB is dedicated to MPIase biosynthesis. A mutant with a high pH-sensitive CdsA8 was unable to grow even under permissive conditions when the ynbB gene was deleted, supporting its auxiliary role in the CdsA function.
MPIase 是一种参与大肠杆菌中蛋白质整合的糖脂。最近，我们鉴定出 CdsA，即 CDP-二酰基甘油（CDP-DAG）合酶，是 MPIase 的生物合成酶。YnbB 是 CdsA 的同工酶，其 C 末端具有高度同源性。在 CdsA 耗尽的条件下，YnbB 的过表达恢复了 MPIase 的表达，但不能恢复磷脂的生物合成。当线粒体 CDP-DAG 合酶 Tam41p 共表达时，YnbB 过表达弥补了 cdsA 敲除突变体的生长缺陷，这表明 YnbB 具有足够的 MPIase 生物合成活性，但没有磷脂生物合成活性。一致地，由 CdsA N 末端和 YnbB C 末端组成的嵌合体（CdsA-N-YnbB-C）本身就可以弥补 cdsA 敲除突变体，但由 YnbB N 末端和 CdsA C 末端组成的嵌合体（YnbB-N-CdsA-C）则需要 Tam41p 的共表达才能进行互补。CdsA 和 CdsA-N-YnbB-C 中的 CDP-DAG 生物合成速率比 YnbB 和 YnbB-N-CdsA-C 中的快得多，这表明 CdsA 的 N 末端加速了 CDP-DAG 的生物合成，从而使细胞快速生长。因此，YnbB 的作用似乎是作为 MPIase 生物合成的备用酶，表明 YnbB 专门用于 MPIase 生物合成。一个具有高 pH 敏感 CdsA8 的突变体即使在 ynbB 基因缺失时也无法在允许条件下生长，这支持了它在 CdsA 功能中的辅助作用。
