The β-barrel membrane protein insertase machinery from Gram-negative bacteria

Noinaj, Nicholas; Rollauer, Sarah E.; Buchanan, Susan K.

doi:10.1016/j.sbi.2015.02.012

Cited by 84 publications

(112 citation statements)

References 34 publications

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“…The overall structure was found in a bent L-shaped conformation, closely resembling that of POTRA3-5 of E. coli BamA (26,39,40). All three POTRA domains contained the conserved βααββ fold observed in other POTRA domains with relatively good structural alignment (23,47,48). Interestingly, the previously observed ∼40-residue insertion within Toc75 POTRA2 (17) overlaps with an extended α-helix encompassing residues 275-296, which we refer to as the P2-helix.…”

Section: Discussionmentioning

confidence: 65%

“…Given the conservation of key features, these structures serve as models for Toc75, albeit with low sequence identity (7%, 7%, and 8%, respectively). Whereas TamA and BamA have roles in the biogenesis of β-barrel outer membrane proteins in Gram-negative bacteria (23,(52)(53)(54)(55), FhaC has a role in the secretion of filamentous hemagglutinin (FHA) out of Bordetella pertussis (56). Here FhaC serves as the translocon within the outer membrane, first interacting with FHA via its TPS domain and then translocating FHA through its barrel domain, across the outer membrane, and into the extracellular milieu.…”

Section: Discussionmentioning

confidence: 99%

“…Omp85 family members are found exclusively in the outer membranes of Gram-negative bacteria, chloroplasts, and mitochondria and have critical roles in outer membrane protein biogenesis and protein transport (19)(20)(21)(22). This family includes β-barrel assembly machinery protein A (BamA) in Gram-negative bacteria (23), and sorting and assembly machinery of 50 kDa (Sam50) in mitochondria (24).…”

mentioning

confidence: 99%

“…BamA, one of the most well-characterized member of this family, has five POTRA domains residing in the periplasm, where they interact with nascent outer membrane protein substrates (23,26), additional components of the BAM complex (Bam B-E), and the periplasmic chaperone, SurA (27). It also has been suggested recently that the BamA POTRAs are involved in modulating the conformation of the BamA β-barrel to promote the insertion of nascent outer membrane proteins (28).…”

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confidence: 99%

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The POTRA domains of Toc75 exhibit chaperone-like function to facilitate import into chloroplasts

O'Neil

Richardson

Paila

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Protein trafficking across membranes is an essential function in cells; however, the exact mechanism for how this occurs is not well understood. In the endosymbionts, mitochondria and chloroplasts, the vast majority of proteins are synthesized in the cytoplasm as preproteins and then imported into the organelles via specialized machineries. In chloroplasts, protein import is accomplished by the TOC (translocon on the outer chloroplast membrane) and TIC (translocon on the inner chloroplast membrane) machineries in the outer and inner envelope membranes, respectively. TOC mediates initial recognition of preproteins at the outer membrane and includes a core membrane channel, Toc75, and two receptor proteins, Toc33/34 and Toc159, each containing GTPase domains that control preprotein binding and translocation. Toc75 is predicted to have a β-barrel fold consisting of an N-terminal intermembrane space (IMS) domain and a C-terminal 16-stranded β-barrel domain. Here we report the crystal structure of the N-terminal IMS domain of Toc75 from Arabidopsis thaliana, revealing three tandem polypeptide transportassociated (POTRA) domains, with POTRA2 containing an additional elongated helix not observed previously in other POTRA domains. Functional studies show an interaction with the preprotein, preSSU, which is mediated through POTRA2-3. POTRA2-3 also was found to have chaperone-like activity in an insulin aggregation assay, which we propose facilitates preprotein import. Our data suggest a model in which the POTRA domains serve as a binding site for the preprotein as it emerges from the Toc75 channel and provide a chaperonelike activity to prevent misfolding or aggregation as the preprotein traverses the intermembrane space.protein import | chloroplast | outer membrane | Toc75 | POTRA domain

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Section: Discussionmentioning

confidence: 65%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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The POTRA domains of Toc75 exhibit chaperone-like function to facilitate import into chloroplasts

O'Neil

Richardson

Paila

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…In Escherichia coli, BamA is the central component of the b-barrel assembly machinery (BAM) complex that performs membrane insertion of OM proteins (OMPs) (7). It consists of the characteristic C-terminal b-barrel and five POTRA domains at the N-terminus.…”

Section: Introductionmentioning

confidence: 99%

Relative Orientation of POTRA Domains from Cyanobacterial Omp85 Studied by Pulsed EPR Spectroscopy

Dastvan

Brouwer

Schuetz

et al. 2016

Biophysical Journal

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Many proteins of the outer membrane of Gram-negative bacteria and of the outer envelope of the endosymbiotically derived organelles mitochondria and plastids have a b-barrel fold. Their insertion is assisted by membrane proteins of the Omp85-TpsB superfamily. These proteins are composed of a C-terminal b-barrel and a different number of N-terminal POTRA domains, three in the case of cyanobacterial Omp85. Based on structural studies of Omp85 proteins, including the five POTRAdomain-containing BamA protein of Escherichia coli, it is predicted that anaP2 and anaP3 bear a fixed orientation, whereas anaP1 and anaP2 are connected via a flexible hinge. We challenged this proposal by investigating the conformational space of the N-terminal POTRA domains of Omp85 from the cyanobacterium Anabaena sp. PCC 7120 using pulsed electron-electron double resonance (PELDOR, or DEER) spectroscopy. The pronounced dipolar oscillations observed for most of the double spinlabeled positions indicate a rather rigid orientation of the POTRA domains in frozen liquid solution. Based on the PELDOR distance data, structure refinement of the POTRA domains was performed taking two different approaches: 1) treating the individual POTRA domains as rigid bodies; and 2) using an all-atom refinement of the structure. Both refinement approaches yielded ensembles of model structures that are more restricted compared to the conformational ensemble obtained by molecular dynamics simulations, with only a slightly different orientation of N-terminal POTRA domains anaP1 and anaP2 compared with the x-ray structure. The results are discussed in the context of the native environment of the POTRA domains in the periplasm.

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Orientation of the OmpF Porin in Planar Lipid Bilayers

et al. 2017

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The outer-membrane protein OmpF is an abundant trimeric general diffusion porin that plays a central role in the transport of antibiotics and colicins across the outer membrane of E. coli. Individual OmpF trimers in planar lipid bilayers (PLBs) show one of two current-voltage asymmetries, thus implying that insertion occurs with either the periplasmic or the extracellular end first. A method for establishing the orientation of OmpF in PLB was developed, based on targeted covalent modification with membrane-impermeant reagents of peripheral cysteine residues introduced near the periplasmic or the extracellular entrance. By correlating the results of the modification experiments with measurements of current asymmetry or the sidedness of binding of the antibiotic enrofloxacin, OmpF orientation could be quickly determined in subsequent experiments under a variety of conditions. Our work will allow the precise interpretation of past and future studies of antibiotic permeation and protein translocation through OmpF and related porins.

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The β-barrel membrane protein insertase machinery from Gram-negative bacteria

Cited by 84 publications

References 34 publications

The POTRA domains of Toc75 exhibit chaperone-like function to facilitate import into chloroplasts

The POTRA domains of Toc75 exhibit chaperone-like function to facilitate import into chloroplasts

Relative Orientation of POTRA Domains from Cyanobacterial Omp85 Studied by Pulsed EPR Spectroscopy

Orientation of the OmpF Porin in Planar Lipid Bilayers

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