TY - JOUR
T1 - Classifying β-barrel assembly substrates by manipulating essential bam complex members
AU - Mahoney, Tara F.
AU - Ricci, Dante P.
AU - Silhavy, Thomas J.
PY - 2016
Y1 - 2016
N2 - The biogenesis of the outer membrane (OM) of Escherichia coli is a conserved and vital process. The assembly of integral β-barrel outer membrane proteins (OMPs), which represent a major component of the OM, depends on periplasmic chaperones and the heteropentameric β-barrel assembly machine (Bam complex) in the OM. However, not all OMPs are affected by null mutations in the same chaperones or nonessential Bam complex members, suggesting there are categories of substrates with divergent requirements for efficient assembly. We have previously demonstrated two classes of substrates, one comprising large, lowabundance, and difficult-to-assemble substrates that are heavily dependent on SurA and also Skp and FkpA, and the other comprising relatively simple and abundant substrates that are not as dependent on SurA but are strongly dependent on BamB for assembly. Here, we describe novel mutations in bamD that lower levels of BamD 10-fold and > 25-fold without altering the sequence of the mature protein. We utilized these mutations, as well as a previously characterized mutation that lowers wildtype BamA levels, to reveal a third class of substrates. These mutations preferentially cause a marked decrease in the levels of multimeric proteins. This susceptibility of multimers to lowered quantities of Bam machines in the cell may indicate that multiple Bam complexes are needed to efficiently assemble multimeric proteins into the OM.
AB - The biogenesis of the outer membrane (OM) of Escherichia coli is a conserved and vital process. The assembly of integral β-barrel outer membrane proteins (OMPs), which represent a major component of the OM, depends on periplasmic chaperones and the heteropentameric β-barrel assembly machine (Bam complex) in the OM. However, not all OMPs are affected by null mutations in the same chaperones or nonessential Bam complex members, suggesting there are categories of substrates with divergent requirements for efficient assembly. We have previously demonstrated two classes of substrates, one comprising large, lowabundance, and difficult-to-assemble substrates that are heavily dependent on SurA and also Skp and FkpA, and the other comprising relatively simple and abundant substrates that are not as dependent on SurA but are strongly dependent on BamB for assembly. Here, we describe novel mutations in bamD that lower levels of BamD 10-fold and > 25-fold without altering the sequence of the mature protein. We utilized these mutations, as well as a previously characterized mutation that lowers wildtype BamA levels, to reveal a third class of substrates. These mutations preferentially cause a marked decrease in the levels of multimeric proteins. This susceptibility of multimers to lowered quantities of Bam machines in the cell may indicate that multiple Bam complexes are needed to efficiently assemble multimeric proteins into the OM.
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U2 - 10.1128/JB.00263-16
DO - 10.1128/JB.00263-16
M3 - Article
C2 - 27161117
AN - SCOPUS:84977636280
VL - 198
SP - 1984
EP - 1992
JO - Journal of Bacteriology
JF - Journal of Bacteriology
SN - 0021-9193
IS - 14
ER -