BrucellaPeriplasmic Protein EipB Is a Molecular Determinant of Cell Envelope Integrity and Virulence
ABSTRACTThe Gram-negative cell envelope is a remarkable structure with core components that include an inner membrane, an outer membrane, and a peptidoglycan layer in the periplasmic space between. Multiple molecular systems function to maintain integrity of this essential barrier between the interior of the cell and its surrounding environment. We show that a conserved DUF1849 family protein, EipB, is secreted to the periplasmic space ofBrucellaspecies, a monophyletic group of intracellular pathogens. In the periplasm, EipB folds into an unusual 14-stranded β-spiral structure that resembles the LolA and LolB lipoprotein delivery system, though the overall fold of EipB is distinct from LolA/LolB. Deletion ofeipBresults in defects inBrucellacell envelope integrityin vitroand in maintenance of spleen colonization in a mouse model ofBrucella abortusinfection. Transposon disruption ofttpA, which encodes a periplasmic protein containing tetratricopeptide repeats, is synthetically lethal witheipBdeletion.ttpAis a reported virulence determinant inBrucella, and our studies ofttpAdeletion and overexpression strains provide evidence that this gene also contributes to cell envelope function. We conclude thateipBandttpAfunction in theBrucellaperiplasmic space to maintain cell envelope integrity, which facilitates survival in a mammalian host.IMPORTANCEBrucellaspecies cause brucellosis, a global zoonosis. A gene encoding a conserved DUF1849-family protein, which we have named EipB, is present in all sequencedBrucellaand several other genera in the classAlphaproteobacteria. The manuscript provides the first functional and structural characterization of a DUF1849 protein. We show that EipB is secreted to the periplasm where it forms a spiral-shaped antiparallel β protein that is a determinant of cell envelope integrityin vitroand 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.