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TatE as a Regular Constituent of Bacterial Twin-arginine Protein Translocases.

ABSTRACT: Twin-arginine translocation (Tat) systems mediate the transmembrane translocation of completely folded proteins that possess a conserved twin-arginine (RR) motif in their signal sequences. Many Tat systems consist of three essential membrane components named TatA, TatB, and TatC. It is not understood why some bacteria, in addition, constitutively express a functional paralog of TatA called TatE. Here we show, in live Escherichia coli cells, that, upon expression of a Tat substrate protein, fluorescently labeled TatE-GFP relocates from a rather uniform distribution in the plasma membrane into a number of discrete clusters. Clustering strictly required an intact RR signal peptide and the presence of the TatABC subunits, suggesting that TatE-GFP associates with functional Tat translocases. In support of this notion, site-specific photo cross-linking revealed interactions of TatE with TatA, TatB, and TatC. The same approach also disclosed a pronounced tendency of TatE and TatA to hetero-oligomerize. Under in vitro conditions, we found that TatE replaces TatA inefficiently. Our collective results are consistent with TatE being a regular constituent of the Tat translocase in E. coli.

SUBMITTER: Eimer E

PROVIDER: S-EPMC4705934 | biostudies-literature | 2015 Dec

REPOSITORIES: biostudies-literature

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TatE as a Regular Constituent of Bacterial Twin-arginine Protein Translocases.

Eimer Ekaterina E Fröbel Julia J Blümmel Anne-Sophie AS Müller Matthias M

The Journal of biological chemistry 20151019 49

Twin-arginine translocation (Tat) systems mediate the transmembrane translocation of completely folded proteins that possess a conserved twin-arginine (RR) motif in their signal sequences. Many Tat systems consist of three essential membrane components named TatA, TatB, and TatC. It is not understood why some bacteria, in addition, constitutively express a functional paralog of TatA called TatE. Here we show, in live Escherichia coli cells, that, upon expression of a Tat substrate protein, fluor ...[more]

PMID: 26483541

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Project description:BackgroundThe twin-arginine translocation (Tat) protein export system enables the transport of fully folded proteins across a membrane. This system is composed of two integral membrane proteins belonging to TatA and TatC protein families and in some systems a third component, TatB, a homolog of TatA. TatC participates in substrate protein recognition through its interaction with a twin arginine leader peptide sequence.Methodology/principal findingsThe aim of this study was to explore TatC diversity, evolution and sequence conservation in bacteria to identify how TatC is evolving and diversifying in various bacterial phyla. Surveying bacterial genomes revealed that 77% of all species possess one or more tatC loci and half of these classes possessed only tatC and tatA genes. Phylogenetic analysis of diverse TatC homologues showed that they were primarily inherited but identified a small subset of taxonomically unrelated bacteria that exhibited evidence supporting lateral gene transfer within an ecological niche. Examination of bacilli tatCd/tatCy isoform operons identified a number of known and potentially new Tat substrate genes based on their frequent association to tatC loci. Evolutionary analysis of these Bacilli isoforms determined that TatCy was the progenitor of TatCd. A bacterial TatC consensus sequence was determined and highlighted conserved and variable regions within a three dimensional model of the Escherichia coli TatC protein. Comparative analysis between the TatC consensus sequence and Bacilli TatCd/y isoform consensus sequences revealed unique sites that may contribute to isoform substrate specificity or make TatA specific contacts. Synonymous to non-synonymous nucleotide substitution analyses of bacterial tatC homologues determined that tatC sequence variation differs dramatically between various classes and suggests TatC specialization in these species.Conclusions/significanceTatC proteins appear to be diversifying within particular bacterial classes and its specialization may be driven by the substrates it transports and the environment of its host.

Project description:BackgroundBacteria and mitochondria contain translocases that function to transport proteins across or insert proteins into their inner and outer membranes. Extant mitochondria retain some bacterial-derived translocases but have lost others. While BamA and YidC were integrated into general mitochondrial protein transport pathways (as Sam50 and Oxa1), the inner membrane TAT translocase, which uniquely transports folded proteins across the membrane, was retained sporadically across the eukaryote tree.ResultsWe have identified mitochondrial TAT machinery in diverse eukaryotic lineages and define three different types of eukaryote-encoded TatABC-derived machineries (TatAC, TatBC and TatC-only). Here, we investigate TatAC and TatC-only machineries, which have not been studied previously. We show that mitochondria-encoded TatAC of the jakobid Andalucia godoyi represent the minimal functional pathway capable of substituting for the Escherichia coli TatABC complex and can transport at least one substrate. However, selected TatC-only machineries, from multiple eukaryotic lineages, were not capable of supporting the translocation of this substrate across the bacterial membrane. Despite the multiple losses of the TatC gene from the mitochondrial genome, the gene was never transferred to the cell nucleus. Although the major constraint preventing nuclear transfer of mitochondrial TatC is likely its high hydrophobicity, we show that in chloroplasts, such transfer of TatC was made possible due to modifications of the first transmembrane domain.ConclusionsAt its origin, mitochondria inherited three inner membrane translocases Sec, TAT and Oxa1 (YidC) from its bacterial ancestor. Our work shows for the first time that mitochondrial TAT has likely retained its unique function of transporting folded proteins at least in those few eukaryotes with TatA and TatC subunits encoded in the mitochondrial genome. However, mitochondria, in contrast to chloroplasts, abandoned the machinery multiple times in evolution. The overall lower hydrophobicity of the Oxa1 protein was likely the main reason why this translocase was nearly universally retained in mitochondrial biogenesis pathways.

Dataset Information

TatE as a Regular Constituent of Bacterial Twin-arginine Protein Translocases.

Publications

TatE as a Regular Constituent of Bacterial Twin-arginine Protein Translocases.

Similar Datasets

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