The big BAM theory: An open and closed case?

Wu, Runrun; Stephenson, Robert E.; Gichaba, Abigail; Noinaj, Nicholas

doi:10.1016/j.bbamem.2019.183062

Cited by 36 publications

(52 citation statements)

References 125 publications

(165 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The in vitro folding pathways of several OMPs have been explored 75,76 , however, how OMP folding is modulated by chaperone binding 28,46,50,58,75 and interactions with BAM remain unresolved 77,78 . Once translocated into the periplasm by the SecYEG complex, OMP folding, comprising delivery to BAM and insertion into the OM, is achieved without an external energy source.…”

Section: Discussionmentioning

confidence: 99%

Inter-domain dynamics in the chaperone SurA and multi-site binding to its outer membrane protein clients

et al. 2020

View full text Add to dashboard Cite

The periplasmic chaperone SurA plays a key role in outer membrane protein (OMP) biogenesis. E. coli SurA comprises a core domain and two peptidylprolyl isomerase domains (P1 and P2), but its mechanisms of client binding and chaperone function have remained unclear. Here, we use chemical cross-linking, hydrogen-deuterium exchange mass spectrometry, single-molecule FRET and molecular dynamics simulations to map the client binding site(s) on SurA and interrogate the role of conformational dynamics in OMP recognition. We demonstrate that SurA samples an array of conformations in solution in which P2 primarily lies closer to the core/P1 domains than suggested in the SurA crystal structure. OMP binding sites are located primarily in the core domain, and OMP binding results in conformational changes between the core/P1 domains. Together, the results suggest that unfolded OMP substrates bind in a cradle formed between the SurA domains, with structural flexibility between domains assisting OMP recognition, binding and release.

show abstract

Section: Discussionmentioning

confidence: 99%

Inter-domain dynamics in the chaperone SurA and multi-site binding to its outer membrane protein clients

et al. 2020

View full text Add to dashboard Cite

show abstract

“…Defects in OMP assembly lead to protein misfolding and aggregation, which link to stress and cellular toxicity in prokaryotes 2 . The insertion and assembly of an OMP into the bacterial outer membrane is a highly regulated process, 3–5 enabled by assistance from periplasmic holdases (e.g., SurA and Skp) and the outer membrane chaperone 4–9 . This phylogenetically conserved transmembrane molecular chaperone is a multiprotein complex referred to as the barrel assembly machinery (BAM) 10 .…”

Section: Introductionmentioning

confidence: 99%

“…The general process of OMP biogenesis and its translocation to the target membrane is fairly well understood in bacteria 7,11,16–18 . Yet, several unresolved ambiguities and open questions exist in the underlying molecular mechanism of OMP assembly and its regulation in the membrane 7,16 .…”

Section: Introductionmentioning

confidence: 99%

Interplay of protein primary sequence, lipid membrane, and chaperone in β‐barrel assembly

Tiwari

Mahalakshmi

2021

Protein Science

View full text Add to dashboard Cite

The outer membrane of a Gram‐negative bacterium is a crucial barrier between the external environment and its internal physiology. This barrier is bridged selectively by β‐barrel outer membrane proteins (OMPs). The in vivo folding and biogenesis of OMPs necessitates the assistance of the outer membrane chaperone BamA. Nevertheless, OMPs retain the ability of independent self‐assembly in vitro. Hence, it is unclear whether substrate–chaperone dynamics is influenced by the intrinsic ability of OMPs to fold, the magnitude of BamA–OMP interdependence, and the contribution of BamA to the kinetics of OMP assembly. We addressed this by monitoring the assembly kinetics of multiple 8‐stranded β‐barrel OMP substrates with(out) BamA. We also examined whether BamA is species‐specific, or nonspecifically accelerates folding kinetics of substrates from independent species. Our findings reveal BamA as a substrate‐independent promiscuous molecular chaperone, which assists the unfolded OMP to overcome the kinetic barrier imposed by the bilayer membrane. We additionally show that while BamA kinetically accelerates OMP folding, the OMP primary sequence remains a vital deciding element in its assembly rate. Our study provides unexpected insights on OMP assembly and the functional relevance of BamA in vivo.

show abstract

“…The periplasmic lipoproteins seem to play important roles in regulating the flow of substrates to BamA and its conformational transitions (25)(26)(27)(28)(29). Although the structure and function of the BAM complex has been studied extensively (19)(20)(21), the mechanism of BAM-mediated OMP insertion is still being elucidated (30,31). A 'membrane thinning' model argues that the asymmetric thickness of the BamA β-barrel thins the OM close to the lateral gate thereby facilitating the spontaneous insertion of OMPs in the OM.…”

Section: Introductionmentioning

confidence: 99%

Spatiotemporal organization of BamA governs the pattern of outer membrane protein distribution in growing Escherichia coli cells

Mamou

Inns

Sun³

et al. 2021

Preprint

View full text Add to dashboard Cite

The outer membrane (OM) of Gram-negative bacteria is a robust protective barrier that excludes major classes of antibiotics. The assembly, integrity and functioning of the OM is dependent on β-barrel outer membrane proteins (OMPs), the insertion of which is catalyzed by BamA, the core component of the β-barrel assembly machine (BAM) complex. Little is known about BamA in the context of its native OM environment. Here, using high-affinity fluorescently-labelled antibodies in combination with diffraction-limited and super-resolution fluorescence microscopy, we uncover the spatial and temporal organization of BamA in live Escherichia coli K-12 cells. BamA is clustered into ~150 nm diameter islands that contain an average of 10-11 BamA molecules, in addition to other OMPs, and are distributed throughout the OM and which migrate to the poles during growth. In stationary phase cells, BamA is largely confined to the poles. Emergence from stationary phase coincides with new BamA-containing islands appearing on the longitudinal axis of cells, suggesting they are not seeded by pre-existing BamAs but initiate spontaneously. Consistent with this interpretation, BamA-catalyzed OMP biogenesis is biased towards non-polar regions. Cells ensure the capacity for OMP biogenesis is uniformly distributed during exponential growth, even if the growth rate changes, by maintaining an invariant density of BamA-containing OMP islands (~9 islands/μm2) that only diminishes as cells enter stationary phase, the latter change governing what OMPs predominate as cells become quiescent. We conclude that OMP distribution in E. coli is driven by the spatiotemporal organisation of BamA which varies with the different phases of growth.SignificanceThe integrity and functioning of the outer membrane (OM) of Gram-negative bacteria depends on the β-barrel assembly machinery (BAM). Although the structure and the mechanism of the complex have been widely explored, little information exists about the organization of the BAM complex and how it dictates protein distribution in the OM. Here, we utilized highly specific monoclonal antibodies to study the spatiotemporal organization of BamA, the key component of this complex. We reveal that BAM organization is dynamic and tightly linked to the cell’s growth phase. We further discover that the rate of BAM facilitated OMP biogenesis is significantly reduced near the poles. In turn, these features govern the biogenesis patterns and the distribution of OMPs on the cell surface.

show abstract

The big BAM theory: An open and closed case?

Cited by 36 publications

References 125 publications

Inter-domain dynamics in the chaperone SurA and multi-site binding to its outer membrane protein clients

Inter-domain dynamics in the chaperone SurA and multi-site binding to its outer membrane protein clients

Interplay of protein primary sequence, lipid membrane, and chaperone in β‐barrel assembly

Spatiotemporal organization of BamA governs the pattern of outer membrane protein distribution in growing Escherichia coli cells

Contact Info

Product

Resources

About