CdsA is involved in biosynthesis of glycolipid MPIase essential for membrane protein integration in vivo

Abstract

MPIase is a glycolipid that is involved in membrane protein integration. Despite evaluation of its functions in vitro, the lack of information on MPIase biosynthesis hampered verification of its involvement in vivo. In this study, we found that depletion of CdsA, a CDP-diacylglycerol synthase, caused not only a defect in phospholipid biosynthesis but also MPIase depletion with accumulation of the precursors of both membrane protein M13 coat protein and secretory protein OmpA. Yeast Tam41p, a mitochondrial CDP-diacylglycerol synthase, suppressed the defect in phospholipid biosynthesis, but restored neither MPIase biosynthesis, precursor processing, nor cell growth, indicating that MPIase is essential for membrane protein integration and therefore for cell growth. Consistently, we observed a severe defect in protein integration into MPIase-depleted membrane vesicles in vitro. Thus, the function of MPIase as a factor involved in protein integration was proven in vivo as well as in vitro. Moreover, Cds1p, a eukaryotic CdsA homologue, showed a potential for MPIase biosynthesis. From these results, we speculate the presence of a eukaryotic MPIase homologue.

Two‐step induction of cdsA promoters leads to upregulation of the glycolipid MPIase at cold temperature

“…The expression levels of the SecYEG translocase and YidC do not change under cold conditions . We have identified and characterized a glycolipid named MPIase (Membrane Protein Integrase), essential for membrane protein integration and therefore cell growth . MPIase is composed of a linear glycan chain comprising 9‐11 repeats of the trisaccharide unit of N ‐acetyl‐D‐glucosamine (GlcNAc), N ‐acetyl‐D‐mannosaminuronic acid and 4‐acetoamido‐4‐deoxy‐D‐fucose, and diacylglycerol through a pyrophosphate linker .…”

“…CDP‐DAG is a precursor of all phospholipids in E. coli . In addition to phospholipid biosynthesis, CdsA also biosynthesizes GlcNAc‐PP‐DAG (Compound I), the first intermediate for MPIase biosynthesis . GlcNAc‐P is substituted by the CMP moiety of CDP‐DAG on CdsA, giving Compound I .…”

“…In addition to phospholipid biosynthesis, CdsA also biosynthesizes GlcNAc‐PP‐DAG (Compound I), the first intermediate for MPIase biosynthesis . GlcNAc‐P is substituted by the CMP moiety of CDP‐DAG on CdsA, giving Compound I . YnbB is a CdsA paralogue dedicated to MPIase biosynthesis .…”

“…first intermediate for MPIase biosynthesis [11]. GlcNAc-P is substituted by the CMP moiety of CDP-DAG on CdsA, giving Compound I [11].…”

“…When both the cdsA and ynbB genes on the chromosome are disrupted, the increase in the MPIase level at low temperature is repressed even if CdsA is expressed from a complementary plasmid, in which cdsA is placed under the control of the arabinose promoter. Furthermore, the expression level of CdsA is upregulated to the same extent as the increase in the MPIase level in the cold [8,11]. These observations indicate that the increase in the MPIase level is regulated by the CdsA level.…”