BrucellaEipB is a periplasmic β-spiral protein required for envelope stress resistance and infection

Abstract

SummaryThe Gram-negative cell envelope is a remarkably diverse structure with core components that include an inner membrane, an outer membrane, and a peptidoglycan layer in the periplasmic space between. We show that a conserved DUF1849-family protein, EipB, is secreted to the periplasmic space ofBrucella, a monophyletic group of intracellular pathogens. In the periplasm, EipB folds into an unusual fourteen-stranded β-spiral structure that contains a conserved disulfide bond. EipB has structural features that resemble the LolA and LolB lipoprotein delivery system, though the overall topology and fold of EipB is distinct from LolA/LolB. Deletion ofeipBresults in defects in both cell envelope integrityin vitroand in maintenance of spleen colonization in a mouse model ofB. abortusinfection. Transposon disruption ofttpA, which encodes a periplasmic tetratricopeptide repeat (TPR) protein, is synthetically lethal witheipBdeletion inB. abortus.ttpAis a known virulence determinant inB. melitensis, and our studies ofttpAdeletion and overexpression strains provide evidence thatttpA, likeeipB, contributes to cell envelope function inBrucella. We conclude thateipBandttpAfunction in theBrucellaperiplasmic space to maintain cell envelope integrity and to facilitate survival in a mammalian host.ImportanceBrucellaspecies cause brucellosis, a global zoonosis. A gene encoding a conserved uncharacterized protein, EipB, is present in all sequencedBrucellaand several other genera in the classAlphaproteobacteria.To our knowledge, this study presents the first functional and structural characterization of a protein from the DUF1849 family, to which EipB belongs. EipB is secreted to the periplasm where it forms a spiral-like anti-parallel β structure. Deletion ofBrucella eipBresults in defects of the cell envelope and in reduced virulence in an animal model of disease.eipBgenetically interacts withttpA, which also encodes a periplasmic protein. We propose that EipB and TtpA function as part of a system required for cell envelope homeostasis in selectAlphaproteobacteria.