Dataset Information

The Bacteroidetes Q-Rule: Pyroglutamate in Signal Peptidase I Substrates.

ABSTRACT: Bacteroidetes feature prominently in the human microbiome, as major colonizers of the gut and clinically relevant pathogens elsewhere. Here, we reveal a new Bacteroidetes specific feature in the otherwise widely conserved Sec/SPI (Sec translocase/signal peptidase I) pathway. In Bacteroidetes, but not the entire FCB group or related phyla, signal peptide cleavage exposes N-terminal glutamine residues in most SPI substrates. Reanalysis of published mass spectrometry data for five Bacteroidetes species shows that the newly exposed glutamines are cyclized to pyroglutamate (also termed 5-oxoproline) residues. Using the dental pathogen Porphyromonas gingivalis as a model, we identify the PG2157 (also called PG_RS09565, Q7MT37) as the glutaminyl cyclase in this species, and map the catalytic activity to the periplasmic face of the inner membrane. Genetic manipulations that alter the glutamine residue immediately after the signal peptide in the pre-pro-forms of the gingipains affect the extracellular proteolytic activity of RgpA, but not RgpB and Kgp. Glutamine statistics, mass spectrometry data and the mutagenesis results show that the N-terminal glutamine residues or their pyroglutamate cyclization products do not act as generic sorting signals.

SUBMITTER: Bochtler M

PROVIDER: S-EPMC5837995 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature

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The Bacteroidetes Q-Rule: Pyroglutamate in Signal Peptidase I Substrates.

Bochtler Matthias M Mizgalska Danuta D Veillard Florian F Nowak Magdalena L ML Houston John J Veith Paul P Reynolds Eric C EC Potempa Jan J

Frontiers in microbiology 20180301

Bacteroidetes feature prominently in the human microbiome, as major colonizers of the gut and clinically relevant pathogens elsewhere. Here, we reveal a new Bacteroidetes specific feature in the otherwise widely conserved Sec/SPI (Sec translocase/signal peptidase I) pathway. In Bacteroidetes, but not the entire FCB group or related phyla, signal peptide cleavage exposes N-terminal glutamine residues in most SPI substrates. Reanalysis of published mass spectrometry data for f ...[more]

PMID: 29545777

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Project description:In Gram-negative didermal species of the phylum Bacteroidetes, the majority of pre(pro)proteins exported across the cell membrane via the Sec system follow the Q-rule: a glutamine residue immediately downstream of a leader peptide is exposed as the new amino terminus by type I signal peptidases and converted to a pyroglutamate (also called oxyproline) residue by an inner membrane-associated glutaminyl cyclase (QC). Here, we show that the QC from Porphyromonas gingivalis is essential for growth in laboratory culture conditions. The lethal phenotype of QC deletion could not be rescued by an inactive variant of the enzyme, but it was rescued by QC orthologues from other species, despite their drastically lower activity toward a fluorescent reporter substrate. Replacement of glutamine after the signal peptide by an asparagine residue in selected QC substrates did not affect P. gingivalis viability but reduced the abundance of these proteins. Our data show that glutaminyl cyclization stabilizes P. gingivalis proteins, presumably protecting them from degradation by aminopeptidases. Loss of this protection is tolerated in individual substrates, but the complete loss in all Q-rule substrates is lethal, even in the absence of pressure from a host immune system. IMPORTANCE Exclusively in the Bacteroidetes phylum, most proteins exported across the inner membrane via the Sec system and released into the periplasm by type I signal peptidase have N-terminal glutamine converted to pyroglutamate. The reaction is catalyzed by the periplasmic enzyme glutaminyl cyclase (QC), which is essential for the growth of Porphyromonas gingivalis and other periodontopathogens. Apparently, pyroglutamyl formation stabilizes extracytoplasmic proteins and/or protects them from proteolytic degradation in the periplasm. Given the role of P. gingivalis as the keystone pathogen in periodontitis, P. gingivalis QC is a promising target for the development of drugs to treat and/or prevent this highly prevalent chronic inflammatory disease leading to tooth loss and associated with severe systemic diseases.

Project description:Signal peptide peptidase-like 3 (Sppl3) is a Golgi-resident intramembrane-cleaving protease that is highly conserved among multicellular eukaryotes pointing to pivotal physiological functions in the Golgi network which are only beginning to emerge. Recently, Sppl3 was shown to control protein N-glycosylation, when the key branching enzyme N-acetylglucosaminyltransferase V (GnT-V) and other medial/trans Golgi glycosyltransferases were identified as first physiological Sppl3 substrates. Sppl3-mediated endoproteolysis releases the catalytic ectodomains of these enzymes from their type II membrane anchors. Protein glycosylation is a multistep process involving numerous type II membrane-bound enzymes, but it remains unclear whether only few of them are Sppl3 substrates or whether Sppl3 cleaves many of them and thereby controls protein glycosylation at multiple levels. Therefore, to systematically identify Sppl3 substrates we used Sppl3-deficient and Sppl3-overexpression cell culture models and analyzed them for changes in secreted membrane protein ectodomains using the proteomics "secretome protein enrichment with click sugars (SPECS)" method. SPECS analysis identified numerous additional new Sppl3 candidate glycoprotein substrates, several of which were biochemically validated as Sppl3 substrates. All novel Sppl3 substrates adopt a type II topology. The majority localizes to the Golgi network and is implicated in Golgi functions. Importantly, most of the novel Sppl3 substrates catalyze the modification of N-linked glycans. Others contribute to O-glycan and in particular glycosaminoglycan biosynthesis, suggesting that Sppl3 function is not restricted to N-glycosylation, but also functions in other forms of protein glycosylation. Hence, Sppl3 emerges as a crucial player of Golgi function and the newly identified Sppl3 substrates will be instrumental to investigate the molecular mechanisms underlying the physiological function of Sppl3 in the Golgi network and in vivo. Data are available via ProteomeXchange with identifier PXD001672.

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The Bacteroidetes Q-Rule: Pyroglutamate in Signal Peptidase I Substrates.

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The <i>Bacteroidetes</i> Q-Rule: Pyroglutamate in Signal Peptidase I Substrates.

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The Bacteroidetes Q-Rule: Pyroglutamate in Signal Peptidase I Substrates.

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