Looks can be deceiving: recent insights into the mechanism of protein secretion by the autotransporter pathway

Bernstein, Harris

doi:10.1111/mmi.13031

Cited by 41 publications

(39 citation statements)

References 96 publications

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“…Based on our results, we propose a more detailed version of a previously described model for autotransporter biogenesis (Bernstein, ). In our model, the C terminus begins to fold into a β barrel‐like structure in the periplasm that incorporates the α‐helical linker segment.…”

Section: Discussionmentioning

confidence: 96%

“…Over 30 years ago, it was proposed that these proteins are autonomous secretion systems in which completely folded β barrel domains transport covalently linked passenger domains across the OM (whence the name 'autotransporter') (Pohlner et al ., 1987 ). Despite the accumulation of evidence that the Bam complex plays a role in the translocation reaction and other findings that have strongly challenged this proposal (Bernstein, 2015 ), however, the self-transport model has persisted (Fan et al ., 2016 ).…”

Section: Introductionmentioning

confidence: 99%

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Identification of a novel post‐insertion step in the assembly of a bacterial outer membrane protein

Peterson

Hussain

Bernstein

2018

Molecular Microbiology

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Although the barrel assembly machinery (Bam) complex has been shown to facilitate the insertion of β barrel proteins into the bacterial outer membrane (OM), the stage at which β barrels fold is unknown. Here, we describe insights into β barrel assembly that emerged from an analysis of a member of the autotransporter family of OM proteins (EspP) in Escherichia coli. EspP contains an extracellular 'passenger' domain that is translocated across the OM and then released from the covalently linked β barrel domain in an intra-barrel cleavage reaction. We found that the mutation of an unusual lipid-exposed lysine residue impairs a previously unidentified late folding step that follows both the membrane insertion of the β barrel domain and the secretion of the passenger domain but that precedes proteolytic maturation. Our results demonstrate that β barrel assembly can be completed at a post-insertion stage and raise the possibility that interactions with membrane lipids can promote folding in vivo. Furthermore, by showing that the passenger domain is secreted before the β barrel domain is fully assembled, our results also provide evidence against the long-standing hypothesis that autotransporters are autonomous protein secretion systems.

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Section: Discussionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Identification of a novel post‐insertion step in the assembly of a bacterial outer membrane protein

Peterson

Hussain

Bernstein

2018

Molecular Microbiology

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“…However, later crystallographic analysis showed that the barrel is not big enough for a passenger translocation, and this prompted a number of mechanistic studies which revealed that the translocation event is coordinated with barrel folding at the Bam complex (38–40; 71). These studies were not only important for our current understanding of the mechanism of autotransporter secretion (reviewed in (4)) but also made several important implications for β-barrel assembly at the Bam complex.…”

Section: Experimental Evidence For β-Barrel Folding At the Periplamentioning

confidence: 99%

Outer Membrane Biogenesis

Konovalova

Kahne²,

Silhavy

2017

Annu. Rev. Microbiol.

247

229

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The hallmark of Gram-negative bacteria and organelles such as mitochondria and chloroplasts is the presence of an outer membrane (OM). In bacteria such as Escherichia coli, the OM is a unique asymmetric lipid bilayer with lipopolysaccharide (LPS) in the outer leaflet. Integral, transmembrane proteins assume a β-barrel structure (OMPs) and their assembly is catalyzed by the heteropentomeric Bam complex containing the OMP BamA and four lipoproteins, BamB-E. How the Bam complex assembles a great diversity of OMPs into a membrane without an obvious energy source is a particularly challenging problem because folding intermediates are predicted to be unstable in either an aqueous or a hydrophobic environment. Two models have been put forward, the budding model based largely on structural data, and the BamA-assisted model based on genetic and biochemical studies. Here we offer a critical discussion of the pros and cons of each.

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“…In addition, recent models of the involvement of BAM in the function of bacterial surface autotransporters include a hybrid two-b-barrel complex that necessarily invokes large conformational rearrangements of BamA during secretion of the autotransporter passenger domains (44).…”

Section: Introductionmentioning

confidence: 99%

BamA POTRA Domain Interacts with a Native Lipid Membrane Surface

Fleming

Patel

et al. 2016

Biophysical Journal

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The outer membrane of Gram-negative bacteria is an asymmetric membrane with lipopolysaccharides on the external leaflet and phospholipids on the periplasmic leaflet. This outer membrane contains mainly β-barrel transmembrane proteins and lipidated periplasmic proteins (lipoproteins). The multisubunit protein β-barrel assembly machine (BAM) catalyzes the insertion and folding of the β-barrel proteins into this membrane. In Escherichia coli, the BAM complex consists of five subunits, a core transmembrane β-barrel with a long periplasmic domain (BamA) and four lipoproteins (BamB/C/D/E). The BamA periplasmic domain is composed of five globular subdomains in tandem called POTRA motifs that are key to BAM complex formation and interaction with the substrate β-barrel proteins. The BAM complex is believed to undergo conformational cycling while facilitating insertion of client proteins into the outer membrane. Reports describing variable conformations and dynamics of the periplasmic POTRA domain have been published. Therefore, elucidation of the conformational dynamics of the POTRA domain in full-length BamA is important to understand the function of this molecular complex. Using molecular dynamics simulations, we present evidence that the conformational flexibility of the POTRA domain is modulated by binding to the periplasmic surface of a native lipid membrane. Furthermore, membrane binding of the POTRA domain is compatible with both BamB and BamD binding, suggesting that conformational selection of different POTRA domain conformations may be involved in the mechanism of BAM-facilitated insertion of outer membrane β-barrel proteins.

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Looks can be deceiving: recent insights into the mechanism of protein secretion by the autotransporter pathway

Cited by 41 publications

References 96 publications

Identification of a novel post‐insertion step in the assembly of a bacterial outer membrane protein

Identification of a novel post‐insertion step in the assembly of a bacterial outer membrane protein

Outer Membrane Biogenesis

BamA POTRA Domain Interacts with a Native Lipid Membrane Surface

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