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Identification of a novel post‐insertion step in the assembly of a bacterial outer membrane protein
Author(s) -
Peterson Janine H.,
Hussain Sunyia,
Bernstein Harris D.
Publication year - 2018
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.14102
Subject(s) - biology , bacterial outer membrane , secretion , protein folding , escherichia coli , microbiology and biotechnology , barrel (horology) , biochemistry , membrane protein , cleavage (geology) , membrane , paleontology , materials science , fracture (geology) , composite material , gene
Summary Although the b arrel a ssembly m achinery (Bam) complex has been shown to facilitate the insertion of β barrel proteins into the bacterial outer membrane (OM), the stage at which β barrels fold is unknown. Here, we describe insights into β barrel assembly that emerged from an analysis of a member of the autotransporter family of OM proteins (EspP) in Escherichia coli . EspP contains an extracellular ‘passenger’ domain that is translocated across the OM and then released from the covalently linked β barrel domain in an intra‐barrel cleavage reaction. We found that the mutation of an unusual lipid‐exposed lysine residue impairs a previously unidentified late folding step that follows both the membrane insertion of the β barrel domain and the secretion of the passenger domain but that precedes proteolytic maturation. Our results demonstrate that β barrel assembly can be completed at a post‐insertion stage and raise the possibility that interactions with membrane lipids can promote folding in vivo. Furthermore, by showing that the passenger domain is secreted before the β barrel domain is fully assembled, our results also provide evidence against the long‐standing hypothesis that autotransporters are autonomous protein secretion systems.