The Sec System: Protein Export in
            <i>Escherichia coli</i>

Crane, Jennine M.; Randall, Linda L.

doi:10.1128/ecosalplus.esp-0002-2017

Cited by 80 publications

(78 citation statements)

References 418 publications

(451 reference statements)

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“…The Sec system exports proteins before they acquire tertiary structure. For Sec-exported proteins, a variety of molecular chaperones and the protein's own signal sequence can help prevent acquisition of tertiary structure (37). Unlike most proteins exported by the Sec, the cytoplasmic chaperone pair GroEL/GroES mediates the export of TEM-1 (38) by binding to and stabilizing the unfolded state (39).…”

Section: Resultsmentioning

confidence: 99%

Collateral fitness effects of mutations

Mehlhoff

Stearns

Rohm

et al. 2019

Preprint

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AbstractThe distribution of fitness effects (DFE) of mutation plays a central role in constraining protein evolution. The underlying mechanisms by which mutations lead to fitness effects are typically attributed to changes in protein specific activity or abundance. Here, we reveal the importance of a mutation’s collateral fitness effects, which we define as effects that do not derive from changes in the protein’s ability to perform its physiological function. We comprehensively measured the collateral fitness effects of missense mutations in the E. coli TEM-1 β-lactamase antibiotic resistance gene using growth competition experiments in the absence of antibiotic. At least 42% of missense mutations in TEM-1 were deleterious, indicating that for some proteins, collateral fitness effects occur as frequently as effects on protein activity and abundance. Deleterious mutations caused improper post-translational processing, incorrect disulfide-bond formation, protein aggregation, changes in gene expression, and pleiotropic effects on cell phenotype. Deleterious collateral fitness effects occurred more frequently in TEM-1 than deleterious effects on antibiotic resistance in environments with low concentrations of the antibiotic. The surprising prevalence of deleterious collateral fitness effects suggests they may play a role in constraining protein evolution, particularly for highly-expressed proteins, for proteins under intermittent selection for their physiological function, and for proteins whose contribution to fitness is buffered against mutations with deleterious effects on protein activity and protein abundance.Significance StatementMutations provide the source of genetic variability upon which evolution acts. Deleterious protein mutations are commonly thought of in terms of how they compromise the protein’s ability to perform its physiological function. However, mutations might also be deleterious if they cause negative effects on one of the countless other cellular processes. The frequency and magnitude of such collateral fitness effects is unknown. Our systematic study of mutations in a bacterial protein finds widespread collateral fitness effects that were associated with protein aggregation, improper protein processing, incomplete protein transport across membranes, incorrect disulfide-bond formation, induction of stress-response pathways, and unexpected changes in cell properties. Our results suggest that deleterious collateral fitness effects may be an important constraint on protein evolution.

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Section: Resultsmentioning

confidence: 99%

Collateral fitness effects of mutations

Mehlhoff

Stearns

Rohm

et al. 2019

Preprint

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“…Thus, the co-translational mode of interaction of SecA with its secreted protein substrates 6 and membrane-spanning proteins 7 is not unprecendented and can contribute to and co-exists with the post-translational mode of targeting and translocation 4 . During post-translational targeting, secretory proteins are captured first by the cytoplasmic homotetrameric export-specific chaperone SecB, which keeps preproteins in a translocation competent partially unfolded state and prevents premature misfolding and degradation 8 . The SecB-preprotein complex is subsequently bound by SecA, a translocation ATPase, which also provides binding sites for preprotein mature domains 9 , anionic phospholipid 10 , SecYEG 11 as well as direct driving force for preprotein translocation through ATP binding and hydrolysis 11,12 .…”

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confidence: 99%

Cardiolipin is required in vivo for the stability of bacterial translocon and optimal membrane protein translocation and insertion

Ryabichko

Ferreira

Vitrac

et al. 2020

Sci Rep

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translocation of preproteins across the Escherichia coli inner membrane requires anionic lipids by virtue of their negative head-group charge either in vivo or in situ. However, available results do not differentiate between the roles of monoanionic phosphatidylglycerol and dianionic cardiolipin (CL) in this essential membrane-related process. To define in vivo the molecular steps affected by the absence of CL in protein translocation and insertion, we analyzed translocon activity, SecYEG stability and its interaction with SecA in an E. coli mutant devoid of CL. Although no growth defects were observed, co-and post-translational translocation of α-helical proteins across inner membrane and the assembly of outer membrane β-barrel precursors were severely compromised in CL-lacking cells. Components of proton-motive force which could impair protein insertion into and translocation across the inner membrane, were unaffected. However, stability of the dimeric SecYEG complex and oligomerization properties of SecA were strongly compromised while the levels of individual SecYEG translocon components, SecA and insertase YidC were largely unaffected. These results demonstrate that CL is required in vivo for the stability of the bacterial translocon and its efficient function in co-translational insertion into and translocation across the inner membrane of E. coli.

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“…SecA, in addition to the SecYEG translocase (38,39) }. This region also exhibits the highest level of genetic variation between the MBL genes, with no fully conserved residues and diverse lengths between 27 and 43 residues (as defined by where the first secondary structure element begins).…”

Section: A Universal Signal Peptide Does Not Fully Abrogate Phenotypimentioning

confidence: 99%

The molecular mechanisms underlying hidden phenotypic variation among metallo-ß-lactamases

Tokuriki

Socha

2018

Preprint

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Genetic variation among orthologous genes has been largely formed through neutral genetic drift to maintain the same functional role. In some circumstances, however, this genetic variation can create critical phenotypic variation, particularly when genes are transferred to a new host by horizontal gene transfer (HGT). Unveiling "hidden phenotypic variation" through HGT is especially important for genes that confer resistance to antibiotics, which continue to disseminate to new organisms through HGT.Despite this biomedical importance, our understanding of the molecular mechanisms that underlie hidden phenotypic variation remains limited. Here we sought to determine the extent of hidden phenotypic variation in the B1 metallo-β-lactamase (MBL) family, as well as to determine its molecular basis by systematically characterizing eight MBL orthologs when they are expressed in three different organisms (E. coli, P. aeruginosa, and K. pneumoniae). We found that these MBLs confer diverse levels of resistance in each organism, which cannot be explained by variation in catalytic efficiency alone; rather, it is the combination of the catalytic efficiency and abundance of functional periplasmic enzyme that best predicts the observed variation in resistance. The level of functional periplasmic expression varied dramatically between MBL orthologs and between hosts.This was the result changes at multiple levels of each enzyme's functional: 1) the quantity of mRNA; 2) the amount of MBL expressed; and 3) the efficacy of functional enzyme translocation to the periplasm. Overall, we see that it is the interaction between each gene and the host's underlying cellular processes (transcription, translation, and translocation) that determines MBL genetic incompatibility thorough HGT. These hostspecific processes may constrain the effective spread and deployment of MBLs to certain host species, and could explain the current observed distribution bias. Author SummaryOrthologous genes spread among different organisms, typically maintaining the same functional role within the cell while accumulating some, presumably functionally-inert, genetic variation over time. However, these seemingly neutral gene sequence changes among orthologs can be revealed to have substantial difference in protein phenotypes, and thus, organismal fitness, when they are transferred to other host species. This socalled "hidden phenotypic variation" through horizontal gene transfer may play an important role in dissemination of antibiotic resistance genes, in particular. In this work, we systematically investigated the extent of phenotypic variation in eight orthologous antibiotic resistant genes from the metallo-β-lactamases family (MBLs), and identified the molecular causes underlying the observed phenotypic variation. We found that functional protein expression varied substantially among MBLs (causing significant variation in the level of antibiotic resistance conferred), and that this could not be explained by variation in catalytic efficiency alone. Instead, we s...

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The Sec System: Protein Export in Escherichia coli

Cited by 80 publications

References 418 publications

Collateral fitness effects of mutations

Collateral fitness effects of mutations

Cardiolipin is required in vivo for the stability of bacterial translocon and optimal membrane protein translocation and insertion

The molecular mechanisms underlying hidden phenotypic variation among metallo-ß-lactamases

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