Structure of the BAM complex and its implications for biogenesis of outer-membrane proteins

Han, Lujia; Zheng, Jianyun; Wang, Yan; Xu, Yang; Liu, Yanqing; Sun, Chuanqi; Cao, Bin; Zhou, Haizhen; Ni, D.R.; Lou, Jizhong; Zhao, Yongfang; Huang, Yihua

doi:10.1038/nsmb.3181

Cited by 183 publications

(254 citation statements)

References 49 publications

Supporting

Mentioning

232

Contrasting

Order By: Relevance

“…In terms of anaP2-anaP3, this is in line with earlier findings on BamA, where the C-terminal POTRA domains ecP3-ecP5 were assumed to have a rigid architecture (36). However, recent crystal structures of assembled BAM complexes challenge this assumption (8)(9)(10). In addition, the orientation of anaP2-anaP3 in the x-ray structure is well within this structure bundle, and thus seems to be a good representative of this ensemble.…”

Section: Discussionsupporting

confidence: 88%

See 1 more Smart Citation

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

Dastvan

Brouwer

Schuetz

et al. 2016

Biophysical Journal

View full text Add to dashboard Cite

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.

show abstract

Section: Discussionsupporting

confidence: 88%

“…However, extrapolating the position of ecP5 from known crystal structures of BamA ( (8,9,28,29)), we propose, to our knowledge, a first model for the relation between flexibility and the dimension of the peptidoglycan layer (PGL, Fig. 6).…”

Section: Discussionmentioning

confidence: 97%

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

Dastvan

Brouwer

Schuetz

et al. 2016

Biophysical Journal

View full text Add to dashboard Cite

show abstract

“…Recent X-ray crystallography and cryo-EM studies reported the structures of several Omp85 family members, including FhaC, TamA, and BamA (28,(36)(37)(38)(43)(44)(45)(46)(47). Given the conservation of key features, these structures serve as models for Toc75, albeit with low sequence identity (7%, 7%, and 8%, respectively).…”

Section: Discussionmentioning

confidence: 99%

“…The structure reveals that the POTRA domains form an L-shaped structure very similar to BamA, with a unique extended helix within POTRA2 that is not observed in the POTRA domains of BamA and other Omp85 family members (25,28,(35)(36)(37)(38). Based on these unique structural properties, we investigated the contribution of individual POTRA repeats in binding chloroplast precursors.…”

mentioning

confidence: 99%

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.

View full text Add to dashboard Cite

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

show abstract

“…Although the structure of the Bam complex was recently solved by both X-ray crystallography and cryo-EM (13)(14)(15)(16), the mechanism by which it catalyzes the integration of b-barrel proteins into the OM remains poorly understood. The complex has the shape of a top hat in which the BamA bbarrel forms the crown and the POTRA domains together with the lipoproteins form a brim (14,15).…”

mentioning

confidence: 99%

The Bam complex catalyzes efficient insertion of bacterial outer membrane proteins into membrane vesicles of variable lipid composition

Hussain

Bernstein

2018

Journal of Biological Chemistry

View full text Add to dashboard Cite

Most proteins that reside in the bacterial outer membrane (OM) have a distinctive "b-barrel" architecture, but the assembly of these proteins is poorly understood. The spontaneous assembly of OM proteins (OMPs) into pure lipid vesicles has been studied extensively, but often requires nonphysiological conditions and time scales and is strongly influenced by properties of the lipid bilayer including surface charge, thickness, and fluidity. Furthermore, the membrane insertion of OMPs in vivo is catalyzed by a heterooligomer called the b-barrel assembly machinery (Bam) complex. To determine the role of lipids in the assembly of OMPs under more physiological conditions, we exploited an assay in which the Bam complex mediates their insertion into membrane vesicles. After reconstituting the Bam complex into vesicles that contain a variety of different synthetic lipids, we found that two model OMPs, EspP and OmpA, folded efficiently regardless of the lipid composition. Most notably, both proteins folded into membranes composed of a gel phase lipid that mimics the rigid bacterial OM. Interestingly, we found that EspP, OmpA and another model protein (OmpG) folded at significantly different rates and that an a-helix embedded inside the EspP b-barrel accelerates folding. Our results show that the Bam complex largely overcomes effects that lipids exert on OMP assembly and suggest that specific interactions between the Bam complex and an OMP influence its rate of folding. __________________________ Gram-negative bacteria, a class that includes many pathogenic and emerging antibiotic-resistant organisms, are bound by a double cell membrane. Most of the proteins that reside in the outer membrane (OM) 2 , which serves as a robust barrier, have a distinctive "b-barrel" architecture. A bbarrel is essentially a b-sheet rolled into a closed cylinder that has a hydrophobic exterior and a hydrophilic interior and that is held together by hydrogen bonds between the first and last bstrands. The b-barrel scaffold is found exclusively in the OM of bacteria and organelles of bacterial origin. OM proteins (OMPs) mediate many different functions vital for bacterial survival and range considerably in size from 8-26 b-strands (1, 2). Some OMPs form oligomers (3), while others contain a segment that is embedded inside the bbarrel or a separately folded domain that is displayed on either the periplasmic or extracellular side of the OM (1).OMPs must first traverse the inner membrane (IM) and the periplasmic space, which is devoid of ATP (4), before they attain their final structure in the OM. After OMPs are transported across the IM in an unfolded conformation through the Sec translocon, a variety of periplasmic chaperones including SurA, Skp, and DegP prevent their aggregation in the periplasm (5-7). Integration into the OM is then catalyzed by the heterooligomeric β-barrel assembly machinery (Bam) complex (8,9). In E. coli, the Bam complex is composed of BamA, a b-barrel protein that contains five http://www.jbc.org/cgi

show abstract

Structure of the BAM complex and its implications for biogenesis of outer-membrane proteins

Cited by 183 publications

References 49 publications

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

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

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

The Bam complex catalyzes efficient insertion of bacterial outer membrane proteins into membrane vesicles of variable lipid composition

Contact Info

Product

Resources

About