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Protein integration into and translocation across biological membranes are vital processes for living cells. The molecular mechanisms underlying these processes are conserved at a fundamental level in all organisms from bacteria to higher plants and animals. Recently, we identified a novel factor involved in protein integration and translocation in the cytoplasmic membrane of E. coli. This factor turned out to be a glycolipid consisting of a glycan chain with a repeating unit of three N-acetylated aminosugars, and diacylglycerol connected through a pyrophosphate linker. After this glycolipid was shown to catalyze protein integration, we named it MPIase (membrane protein integrase). MPIase drives protein integration by directly interacting with membrane proteins like a molecular chaperone dedicated to membrane proteins. From this function of MPIase, we proposed the concept of ‘glycolipozyme’. We also found that during protein translocation MPIase modulates the structure of SecYEG, a protein-conducting channel. Thus, MPIase possesses critical functions in both protein translocation and integration, suggesting the presence of eukaryotic MPIase homologues. Possible interaction of MPIase with components of the protein transport machinery, including SecYEG and YidC, will be discussed.