Distinctive Roles for Periplasmic Proteases in the Maintenance of Essential Outer Membrane Protein Assembly.

TitleDistinctive Roles for Periplasmic Proteases in the Maintenance of Essential Outer Membrane Protein Assembly.
Publication TypeJournal Article
Year of Publication2017
AuthorsSoltes, GR, Martin, NR, Park, E, Sutterlin, HA, Silhavy, TJ
JournalJ Bacteriol
Volume199
Issue20
Date Published2017 10 15
ISSN1098-5530
KeywordsBacterial Outer Membrane Proteins, Escherichia coli, Escherichia coli Proteins, Heat-Shock Proteins, Metalloproteases, Models, Biological, Peptide Hydrolases, Periplasmic Proteins, Proteolysis, Serine Endopeptidases
Abstract

<p>Outer membrane protein (OMP) biogenesis in is a robust process essential to the life of the organism. It is catalyzed by the β-barrel assembly machine (Bam) complex, and a number of quality control factors, including periplasmic chaperones and proteases, maintain the integrity of this trafficking pathway. Little is known, however, about how periplasmic proteases recognize and degrade OMP substrates when assembly is compromised or whether different proteases recognize the same substrate at distinct points in the assembly pathway. In this work, we use well-defined assembly-defective mutants of LptD, the essential lipopolysaccharide assembly translocon, to show that the periplasmic protease DegP degrades substrates with assembly defects that prevent or impair initial contact with Bam, causing the mutant protein to accumulate in the periplasm. In contrast, another periplasmic protease, BepA, degrades a LptD mutant substrate that has engaged the Bam complex and formed a nearly complete barrel. Furthermore, we describe the role of the outer membrane lipoprotein YcaL, a protease of heretofore unknown function, in the degradation of a LptD substrate that has engaged the Bam complex but is stalled at an earlier step in the assembly process that is not accessible to BepA. Our results demonstrate that multiple periplasmic proteases monitor OMPs at distinct points in the assembly process. OMP assembly is catalyzed by the essential Bam complex and occurs in a cellular environment devoid of energy sources. Assembly intermediates that misfold can compromise this essential molecular machine. Here we demonstrate distinctive roles for three different periplasmic proteases that can clear OMP substrates with folding defects that compromise assembly at three different stages. These quality control factors help ensure the integrity of the permeability barrier that contributes to the intrinsic resistance of Gram-negative organisms to many antibiotics.</p>

DOI10.1128/JB.00418-17
Alternate JournalJ Bacteriol
PubMed ID28784813
PubMed Central IDPMC5637175
Grant ListR01 GM034821 / GM / NIGMS NIH HHS / United States
R35 GM118024 / GM / NIGMS NIH HHS / United States
T32 GM007388 / GM / NIGMS NIH HHS / United States