These phenotypic characteristics suggest that the BamD C-terminus, although nonessential, fulfills some functional Bindarit solubility dmso requirement for Neisseria and for E. coli (and likely for other proteobacteria) that is either unnecessary for B. burgdorferi, or is provided by a different protein. Interestingly, it has been shown that the C-terminus of the E. coli BamD binds BamC and BamE, and is therefore important for the stability of this part of the BAM complex [11, 19, 21, 24, 59]. Thus, a truncated B. burgdorferi BamD may simply be the result of this organism having no requirement for an extended C-terminal region to interact with additional accessory Volasertib mouse lipoproteins such

as BamC or BamE, since we were not able to identify other accessory lipoproteins in B. burgdorferi. Conclusions In the current study, we have identified two accessory components of the B. burgdorferi BAM complex. Based on the knowledge gained from studying other proteobacterial organisms, it is possible that B. burgdorferi contains one or more other BAM accessory lipoprotein components

in addition to BB0324 and BB0028 that are still unidentified. As indicated by BN-PAGE in Figure 1A, multiple high molecular weight (MW) complexes containing BamA are present between approximately 148 kDa and over 1,000 kDa. These data accommodate the possibility that additional protein species may be co-migrating with BamA, especially since the smallest of the two most prominent bands, which migrates at ~200 kDa, has an approximate MW that EX 527 cell line is larger than the expected MW of BamA, BB0028, and BB0324 CHIR-99021 in vitro combined (~144 kDa). Alternatively, these large protein complexes may contain multiple copies of the same protein, such as multiple BB0324 molecules, and/or be homo-oligomers of the entire BAM complex. It should be noted, however, that B. burgdorferi contains a relatively small number of integral OMPs (at least 10-fold

fewer) compared to E. coli [60, 61]; hence, it may require a less complicated BAM complex system for OMP assembly. Indeed, Silhavy and coworkers proposed that the major function of the nonessential E. coli BamB, BamC, and BamE lipoproteins is most likely to increase efficiency of OMP assembly, or to stabilize the complex, since individual mutants were viable and showed relatively mild assembly defects [11, 19, 26]. It is, therefore, possible that an OM with a more limited OMP repertoire, such as that of B. burgdorferi, does not necessitate additional BAM complex members to provide the essential functions for complete OM biogenesis. In this regard, it is tempting to speculate that the B. burgdorferi BAM constituents identified here constitute a “”minimal”" bacterial BAM complex, which can now be further studied as a model system to not only further our understanding of B.