title: MPIase is a glycolipozyme essential for membrane protein integration.
abstract: Protein integration into biological membranes is a vital cellular event for all organisms. We previously reported an integration factor in the inner membrane of Escherichia coli, named MPIase (membrane protein integrase). Here we show that in contrast to previously identified integration factors that are proteins, MPIase is a glycolipid composed of diacylglycerol and a glycan chain of three acetylated aminosugars linked through pyrophosphate. Hydrolytic removal of the lipid moiety gives a soluble product with higher integration activity than that of the original MPIase. This soluble form of MPIase directly interacts with a newborn membrane protein, maintaining its integration-competent structure and allowing its post-translational integration. MPIase actively drives protein integration following chaperoning membrane proteins. We further demonstrate with anti-MPIase antibodies that MPIase is likely involved in integration in vivo. Collectively, our results suggest that MPIase, essential for membrane protein integration, is to our knowledge the first glycolipid with an enzyme-like activity.
authors.affiliation: Cryobiofrontier Research Center, Faculty of Agriculture, Iwate University, 3-18-8 Ueda, Morioka, Iwate                 020-8550, Japan.
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Nishiyama
authors.forename: Masahide
authors.initials: M
authors.lastname: Maeda
authors.forename: Kayo
authors.initials: K
authors.lastname: Yanagisawa
authors.forename: Ryohei
authors.initials: R
authors.lastname: Nagase
authors.forename: Hajime
authors.initials: H
authors.lastname: Komura
authors.forename: Takashi
authors.initials: T
authors.lastname: Iwashita
authors.forename: Tohru
authors.initials: T
authors.lastname: Yamagaki
authors.forename: Shoichi
authors.initials: S
authors.lastname: Kusumoto
authors.forename: Hajime
authors.initials: H
authors.lastname: Tokuda
authors.forename: Keiko
authors.initials: K
authors.lastname: Shimamoto
mesh_terms: D004926:Escherichia coli / Q000201:enzymology* / Q000378:metabolism / Q000502:physiology; D006017:Glycolipids / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism* / Q000502:physiology; D018832:Molecular Chaperones / Q000378:metabolism / Q000502:physiology; D011499:Protein Processing, Post-Translational / Q000502:physiology; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013329:Structure-Activity Relationship
chemical_list: D006017:Glycolipids; D008565:Membrane Proteins; D018832:Molecular Chaperones