The TAM: A Translocation and Assembly Module of the β-barrel Assembly Machinery in Bacterial Outer Membranes

Stubenrauch, Christopher J.; Lithgow, Trevor

doi:10.1128/9781683670285.ch9

Cited by 7 publications

(11 citation statements)

References 48 publications

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“…In an apparent divergence, however, the usually essential BamD was dispensable for borrelial growth, while depletion of the generally auxiliary BamB led to a detectable growth defect (78)(79)(80). B. burgdorferi BamA also was shown to interact with a TamB (BB0794) homolog that in other bacteria is part of a parallel OMP Translocation and Assembly Module (TAM) pathway (69,81). This indicates that B. burgdorferi has adapted modules of separate secretion machineries to function in a single hybrid pathway (82).…”

Section: Insertion and Topology Of Integral Outer Membrane Proteins (Omps)mentioning

confidence: 99%

Protein Secretion in Spirochetes

Zückert

2019

Microbiol Spectr

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Spirochetes form a separate phylum of bacteria with two membranes but otherwise unusual morphologies and envelope structures. Distinctive common features of Borrelia, Leptospira and Treponema include the sequestration of flagella to the periplasm and thin peptidoglycan cell walls that are more closely associated with the inner membrane. Outer membrane compositions differ significantly between the genera. Leptospira most closely track gram-negative bacteria due to the incorporation of lipopolysaccharides. Treponema and Borrelia outer membranes lack lipopolysaccharide, with treponemes expressing only few outer membrane proteins, and Borrelia displaying a dizzying diversity of abundant surface lipoproteins instead. Phylogenetic and experimental evidence indicates that spirochetes have adapted various modules of bacterial export and secretion pathways to build and maintain their envelopes. Export and insertion pathways in the inner membrane appear conserved, while spirochetal experimentation with various envelope architectures over time has led to variations in secretion pathways in the periplasm and outer membrane. Classical type I-III secretion systems have been identified, with demonstrated roles in drug efflux and export of flagellar proteins only. Unique activities of periplasmic proteases, including a C-terminal protease, are involved in maturation of some periplasmic proteins. Proper lipoprotein sorting within the periplasm appears to dependent on functional Lol pathways that lack the outer membrane lipoprotein insertase LolB. The abundance of surface lipoproteins in Borrelia and detailed protein sorting studies suggest a lipoprotein secretion pathway that either extends Lol through the outer membrane or bypasses it altogether. Proteins can be released from cells in outer membrane vesicles, or rarely as soluble proteins.

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Section: Insertion and Topology Of Integral Outer Membrane Proteins (Omps)mentioning

confidence: 99%

Protein Secretion in Spirochetes

Zückert

2019

Microbiol Spectr

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“…OmpA is estimated to have >100,000 copies in the OM of E. coli , whereas OmpX, OmpC, and OmpF are estimated to have >20,000 copies each) ( 3 – 7 ). The functions of OMPs are also very diverse, including passive pores and ion channels ( 8 – 11 ), antibiotic efflux channels ( 12 – 15 ), nutrient uptake systems ( 16 – 18 ), maintenance of structural integrity ( 19 – 21 ), biogenesis and upkeep of the OM ( 22 – 26 ), host cell adhesion and invasion ( 27 – 29 ), biofilm formation ( 30 – 33 ), and cell defense ( 34 , 35 ). Despite the enormous diversity of OMPs in E. coli , it is perhaps surprising that only two are essential: the 16-stranded BamA and 26-stranded LptD ( 36 ) ( Fig.…”

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confidence: 99%

Role of the lipid bilayer in outer membrane protein folding in Gram-negative bacteria

Horne

Brockwell

Radford

2020

Journal of Biological Chemistry

122

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β-barrel outer membrane proteins (OMPs) represent the major proteinaceous component of the outer membrane (OM) of Gram-negative bacteria. These proteins perform key roles in cell structure and morphology, nutrient acquisition, colonisation and invasion, and protection against external toxic threats such as antibiotics. To become functional, OMPs must fold and insert into a crowded and asymmetric OM that lacks much freely accessible lipid. This feat is accomplished in the absence of an external energy source and is thought to be driven by the high thermodynamic stability of folded OMPs in the OM. With such a stable fold, the challenge that bacteria face in assembling OMPs into the OM is how to overcome the initial energy barrier of membrane insertion. In this review, we highlight the roles of the lipid environment and the OM in modulating the OMP folding landscape and discuss the factors that guide folding in vitro and in vivo. We particularly focus on the composition, architecture and physical properties of the OM and how an understanding of the folding properties of OMPs in vitro can help explain the challenges they encounter during folding in vivo. Current models of OMP biogenesis in the cellular environment are still in flux, but the stakes for improving the accuracy of these models are high. Since OMP folding is an essential process in all Gram-negative bacteria, and considering the looming crisis of widespread microbial drug resistance, to bring down the powerful, OMP-supported barrier against antibiotics, we must first understand how bacterial cells build it.

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“…T5SS proteins exported by the Sec translocon emerge in the periplasm, with their N-terminus first, in an unfolded conformation. The translocator domains must then reach the outer membrane, in which they are inserted/folded by the BAM (β-barrel assembly machinery) or TAM (translocation and assembly module) machineries [ 85 , 86 , 87 ]. Meanwhile, the long passenger domains must be prevented from aggregation and degradation and maintained in a conformation competent for proper translocation across the OM.…”

Section: Periplasmic Transitmentioning

confidence: 99%

Folding Control in the Path of Type 5 Secretion

Dautin

2021

Toxins

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The type 5 secretion system (T5SS) is one of the more widespread secretion systems in Gram-negative bacteria. Proteins secreted by the T5SS are functionally diverse (toxins, adhesins, enzymes) and include numerous virulence factors. Mechanistically, the T5SS has long been considered the simplest of secretion systems, due to the paucity of proteins required for its functioning. Still, despite more than two decades of study, the exact process by which T5SS substrates attain their final destination and correct conformation is not totally deciphered. Moreover, the recent addition of new sub-families to the T5SS raises additional questions about this secretion mechanism. Central to the understanding of type 5 secretion is the question of protein folding, which needs to be carefully controlled in each of the bacterial cell compartments these proteins cross. Here, the biogenesis of proteins secreted by the Type 5 secretion system is discussed, with a focus on the various factors preventing or promoting protein folding during biogenesis.

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The TAM: A Translocation and Assembly Module of the β-barrel Assembly Machinery in Bacterial Outer Membranes

Cited by 7 publications

References 48 publications

Protein Secretion in Spirochetes

Protein Secretion in Spirochetes

Role of the lipid bilayer in outer membrane protein folding in Gram-negative bacteria

Folding Control in the Path of Type 5 Secretion

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