TY - JOUR
T1 - Functions of the BamBCDE lipoproteins revealed by bypass mutations in BamA
AU - Hart, Elizabeth M.
AU - Silhavy, Thomas J.
N1 - Funding Information:
We thank members of the Silhavy laboratory for productive discussion. Research performed in this publication was supported by the National Institute of General Medical Sciences of the National Institutes of Health under grant number R35-GM118024 (to T.J.S.) and R01-GM034821 (to T.J.S.). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. E.M.H. and T.J.S. designed the research. E.M.H. performed the research. E.M.H. and T.J.S. wrote the manuscript. We declare no competing interests.
Publisher Copyright:
© 2020 American Society for Microbiology.
PY - 2020/10/8
Y1 - 2020/10/8
N2 - The heteropentomeric β-barrel assembly machine (BAM complex) is responsible for folding and inserting a diverse array of β-barrel outer membrane proteins (OMPs) into the outer membrane (OM) of Gram-negative bacteria. The BAM complex contains two essential proteins, the β-barrel OMP BamA and a lipoprotein BamD, whereas the auxiliary lipoproteins BamBCE are individually nonessential. Here, we identify and characterize three bamA mutations, the E-to-K change at position 470 (bamAE470K), the A-to-P change at position 496 (bamAA496P), and the A-to-S change at position 499 (bamAA499S), that suppress the otherwise lethal ΔbamD, ΔbamB ΔbamC ΔbamE, and ΔbamC ΔbamD ΔbamE mutations. The viability of cells lacking different combinations of BAM complex lipoproteins provides the opportunity to examine the role of the individual proteins in OMP assembly. Results show that, in wild-type cells, BamBCE share a redundant function; at least one of these lipoproteins must be present to allow BamD to coordinate productively with BamA. Besides BamA regulation, BamD shares an additional essential function that is redundant with a second function of BamB. Remarkably, bamAE470K suppresses both, allowing the construction of a BAM complex composed solely of BamAE470K that is able to assemble OMPs in the absence of BamBCDE. This work demonstrates that the BAM complex lipoproteins do not participate in the catalytic folding of OMP substrates but rather function to increase the efficiency of the assembly process by coordinating and regulating the assembly of diverse OMP substrates.
AB - The heteropentomeric β-barrel assembly machine (BAM complex) is responsible for folding and inserting a diverse array of β-barrel outer membrane proteins (OMPs) into the outer membrane (OM) of Gram-negative bacteria. The BAM complex contains two essential proteins, the β-barrel OMP BamA and a lipoprotein BamD, whereas the auxiliary lipoproteins BamBCE are individually nonessential. Here, we identify and characterize three bamA mutations, the E-to-K change at position 470 (bamAE470K), the A-to-P change at position 496 (bamAA496P), and the A-to-S change at position 499 (bamAA499S), that suppress the otherwise lethal ΔbamD, ΔbamB ΔbamC ΔbamE, and ΔbamC ΔbamD ΔbamE mutations. The viability of cells lacking different combinations of BAM complex lipoproteins provides the opportunity to examine the role of the individual proteins in OMP assembly. Results show that, in wild-type cells, BamBCE share a redundant function; at least one of these lipoproteins must be present to allow BamD to coordinate productively with BamA. Besides BamA regulation, BamD shares an additional essential function that is redundant with a second function of BamB. Remarkably, bamAE470K suppresses both, allowing the construction of a BAM complex composed solely of BamAE470K that is able to assemble OMPs in the absence of BamBCDE. This work demonstrates that the BAM complex lipoproteins do not participate in the catalytic folding of OMP substrates but rather function to increase the efficiency of the assembly process by coordinating and regulating the assembly of diverse OMP substrates.
KW - BAM complex
KW - Escherichia coli
KW - Gram-negative bacteria
KW - Outer membrane
KW - Outer membrane biogenesis
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U2 - 10.1128/JB.00401-20
DO - 10.1128/JB.00401-20
M3 - Article
C2 - 32817097
AN - SCOPUS:85092749736
SN - 0021-9193
VL - 202
JO - Journal of Bacteriology
JF - Journal of Bacteriology
IS - 21
M1 - e00401-20
ER -