Biosynthesis of glycolipid MPIase (membrane protein integrase) is independent of the genes for ECA (enterobacterial common antigen)

Abstract

MPIase (membrane protein integrase) is an essential glycolipid that drives protein integration into the inner membrane of E. coli, while glycolipid ECA (enterobacterial common antigen) is a major component at the surface of the outer membrane. Irrespective of the differences in molecular weight, subcellular localization and function in cells, the glycan chains of the two glycolipids are similar, since the repeating unit comprising the glycan chains is the same. A series of biosynthetic genes for ECA, including ones for the corresponding nucleotide sugars, have been identified and extensively characterized. In this study, we found that knockouts as to the respective genes for ECA biosynthesis can grow in the minimum medium with the normal expression level of MPIase, indicating that MPIase can be biosynthesized de novo without the utilization of any compounds generated through ECA biosynthesis. Conversely, ECA was expressed normally upon MPIase depletion. From these results, we conclude that the biosynthetic genes for MPIase and ECA are independent.