title: BB0324 and BB0028 are constituents of the Borrelia burgdorferi β-barrel assembly machine (BAM) complex.
abstract: BACKGROUND
  Similar to Gram-negative bacteria, the outer membrane (OM) of the pathogenic spirochete, Borrelia burgdorferi, contains integral OM-spanning proteins (OMPs), as well as membrane-anchored lipoproteins. Although the mechanism of OMP biogenesis is still not well-understood, recent studies have indicated that a heterooligomeric OM protein complex, known as BAM (β-barrel assembly machine) is required for proper assembly of OMPs into the bacterial OM. We previously identified and characterized the essential β-barrel OMP component of this complex in B. burgdorferi, which we determined to be a functional BamA ortholog.
  
  
  RESULTS
  In the current study, we report on the identification of two additional protein components of the B. burgdorferi BAM complex, which were identified as putative lipoproteins encoded by ORFs BB0324 and BB0028. Biochemical assays with a BamA-depleted B. burgdorferi strain indicate that BB0324 and BB0028 do not readily interact with the BAM complex without the presence of BamA, suggesting that the individual B. burgdorferi BAM components may associate only when forming a functional BAM complex. Cellular localization assays indicate that BB0324 and BB0028 are OM-associated subsurface lipoproteins, and in silico analyses indicate that BB0324 is a putative BamD ortholog.
  
  
  CONCLUSIONS
  The combined data suggest that the BAM complex of B. burgdorferi contains unique protein constituents which differ from those found in other proteobacterial BAM complexes. The novel findings now allow for the B. burgdorferi BAM complex to be further studied as a model system to better our understanding of spirochetal OM biogenesis in general.
authors.affiliation: Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
authors.forename: Tiffany R
authors.initials: TR
authors.lastname: Lenhart
authors.forename: Melisha R
authors.initials: MR
authors.lastname: Kenedy
authors.forename: Xiuli
authors.initials: X
authors.lastname: Yang
authors.forename: Utpal
authors.initials: U
authors.lastname: Pal
authors.forename: Darrin R
authors.initials: DR
authors.lastname: Akins
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000096:biosynthesis*; D025065:Borrelia burgdorferi / Q000378:metabolism*; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000096:biosynthesis*; D016366:Open Reading Frames; D017434:Protein Structure, Tertiary
chemical_list: D001425:Bacterial Outer Membrane Proteins; D046912:Multiprotein Complexes