Characterization of the β-barrel assembly machine accessory lipoproteins from Borrelia burgdorferi

BMC Microbiology

Darrin R Akins¹  Henna Iqbal¹  Melisha R Kenedy¹  Joshua P Dunn¹ 

[1]Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City 73104, OK, USA

关键词: BamD;    BamB;    BamA;    Lipoproteins;    BAM complex;    Lyme disease;    Borrelia burgdorferi;   

Others  :  1212081
DOI  :  10.1186/s12866-015-0411-y

 received in 2015-01-14, accepted in 2015-03-12,  发布年份 2015

【 摘 要 】

Background

Like all diderm bacteria studied to date, Borrelia burgdorferi possesses a β-barrel assembly machine (BAM) complex. The bacterial BAM complexes characterized thus far consist of an essential integral outer membrane protein designated BamA and one or more accessory proteins. The accessory proteins are typically lipid-modified proteins anchored to the inner leaflet of the outer membrane through their lipid moieties. We previously identified and characterized the B. burgdorferi BamA protein in detail and more recently identified two lipoproteins encoded by open reading frames bb0324 and bb0028 that associate with the borrelial BamA protein. The role(s) of the BAM accessory lipoproteins in B. burgdorferi is currently unknown.

Results

Structural modeling of B. burgdorferi BB0028 revealed a distinct β-propeller fold similar to the known structure for the E. coli BAM accessory lipoprotein BamB. Additionally, the structural model for BB0324 was highly similar to the known structure of BamD, which is consistent with the prior finding that BB0324 contains tetratricopeptide repeat regions similar to other BamD orthologs. Consistent with BB0028 and BB0324 being BAM accessory lipoproteins, mutants lacking expression of each protein were found to exhibit altered membrane permeability and enhanced sensitivity to various antimicrobials. Additionally, BB0028 mutants also exhibited significantly impaired in vitro growth. Finally, immunoprecipitation experiments revealed that BB0028 and BB0324 each interact specifically and independently with BamA to form the BAM complex in B. burgdorferi.

Conclusions

Combined structural studies, functional assays, and co-immunoprecipitation experiments confirmed that BB0028 and BB0324 are the respective BamB and BamD orthologs in B. burgdorferi, and are important in membrane integrity and/or outer membrane protein localization. The borrelial BamB and BamD proteins both interact specifically and independently with BamA to form a tripartite BAM complex in B. burgdorferi. A working model has been developed to further analyze outer membrane biogenesis and outer membrane protein transport in this pathogenic spirochete.

【 授权许可】

   
2015 Dunn et al.; licensee BioMed Central.

【 图 表 】

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