Biosynthesis of the proteasome inhibitor syringolin A: the ureido group joining two amino acids originates from bicarbonate

Ramel, Christina; Tobler, Micha; Meyer, Martin; Bigler, Laurent; Ebert, Marc‐Olivier; Schellenberg, Barbara; Dudler, Robert

doi:10.1186/1471-2091-10-26

Cited by 37 publications

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“…Further research will be required to determine the contribution of syrbactins and other proteasome inhibitors to the virulence of pathogens. [56,57]. The first NRPS module of SylD is thought to activate lysine (Lys), which is desaturated to 3,4-dehydrolysine by the sylB gene product [43].…”

Section: Discussionmentioning

confidence: 99%

“…Sequence and architecture of these genes implied a SylA biosynthesis model also experimentally supported in most of its aspects [54][55][56][57][58] (Figure 2B). Importantly, the structure of SylA with its 12-membered macrolactam ring containing the functional α,β-unsaturated carbonyl group is reflected in the unique architecture of the sylD gene.…”

Section: A T3e With Proteasome Inhibiting Activitymentioning

confidence: 99%

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The role of bacterial phytotoxins in inhibiting the eukaryotic proteasome

Dudler

2014

Trends in Microbiology

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The ubiquitin-26S proteasome degradation system (UPS) plays a pivotal role in almost all aspects of plant life, including defending against pathogens. Although the proteasome is important for plant immunity, it has been found to be also exploited by pathogens using effectors to increase their virulence. Recent work on the XopJ effector and syringolin A/syrbactins has highlighted host proteasome inhibition as a virulence strategy of pathogens. This review will focus on these recent developments. AbstractThe ubiquitin-26S proteasome degradation system (UPS) plays a pivotal role in almost all aspects of plant life, including defending against pathogens. While the proteasome is important for plant immunity, it has been found to also be exploited by pathogens using effectors to increase their virulence. Recent work on the XopJ effector and syringolin A/syrbactins has highlighted host proteasome inhibition as a virulence strategy of pathogens. This review will focus on these recent developments. The ubiquitin-26S proteasome degradation system (UPS) and plant immunityBesides the lysosome, the UPS is the main protein degradation system of eukaryotic cells that not only destructs misfolded proteins but is also involved in many cellular processes by degrading proteins regulating such processes [1,2]. Proteins destined for destruction by the proteasome become polyubiquitinated by a reaction cascade involving three enzymes designated E1, E2, and E3. Ubiquitin is activated in an ATP-dependent way by E1 and transferred to E2, from which it is normally directly transferred to a lysine residue of the target protein by E3, which, by selecting target proteins, confers specificity to the UPS [3].Polyubiquitination is achieved by multiple rounds in which further ubiquitin units are conjugated to an internal lysine residue of ubiquitin. Polyubiquitinated proteins are substrates for the proteasome, which is composed of two 19S regulatory particles (RP) capping a 20S core particle (CP). The RPs recognize polyubiquitinated proteins, which become deubiquitinated and unfolded in an ATP-dependent reaction, and regulate access of unfolded substrates to the proteolytic channel of the CP. The channel is formed by four stacked sevenmembered rings. The two identical outer rings consist of seven different α-subunits, whereas 3 the two identical inner rings consist of seven different β-subunits, three of which have proteolytic activities: the β1 subunit exhibits a caspase-like activity (CL), cleaving protein substrates after acidic residues, while the β2 and β5 subunits have trypsin-like (TL) and chymotrypsin-like (ChTL) activities cleaving after basic and hydrophobic residues, respectively. In all three catalytic subunits, the active site residue is the N-terminal threonineThe UPS is involved in the signaling pathways of nearly all plant hormones, including salicylic acid (SA), jasmonic acid (JA), and ethylene (ET), hormones of particular importance for plant defense against pathogens [5]. SA plays a prominent role in defense reactio...

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Section: Discussionmentioning

confidence: 99%

Section: A T3e With Proteasome Inhibiting Activitymentioning

confidence: 99%

The role of bacterial phytotoxins in inhibiting the eukaryotic proteasome

Dudler

2014

Trends in Microbiology

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“…The dipeptide tail contains two L-Vals, linked through an ureido bond. SylA is produced by Psy by nonribosomal peptide and polyketide synthetases encoded by the sylC and sylD biosynthesis genes and presumably secreted from bacteria by the product of sylE, which encodes a transporter-like protein (Amrein et al, 2004;Imker et al, 2009;Ramel et al, 2009).…”

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Proteasome Activity Imaging and Profiling Characterizes Bacterial Effector Syringolin A

et al. 2010

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Syringolin A (SylA) is a nonribosomal cyclic peptide produced by the bacterial pathogen Pseudomonas syringae pv syringae that can inhibit the eukaryotic proteasome. The proteasome is a multisubunit proteolytic complex that resides in the nucleus and cytoplasm and contains three subunits with different catalytic activities: b1, b2, and b5. Here, we studied how SylA targets the plant proteasome in living cells using activity-based profiling and imaging. We further developed this technology by introducing new, more selective probes and establishing procedures of noninvasive imaging in living Arabidopsis (Arabidopsis thaliana) cells. These studies showed that SylA preferentially targets b2 and b5 of the plant proteasome in vitro and in vivo. Structure-activity analysis revealed that the dipeptide tail of SylA contributes to b2 specificity and identified a nonreactive SylA derivative that proved essential for imaging experiments. Interestingly, subcellular imaging with probes based on epoxomicin and SylA showed that SylA accumulates in the nucleus of the plant cell and suggests that SylA targets the nuclear proteasome. Furthermore, subcellular fractionation studies showed that SylA labels nuclear and cytoplasmic proteasomes. The selectivity of SylA for the catalytic subunits and subcellular compartments is discussed, and the subunit selectivity is explained by crystallographic data.

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“…Whereas the abundance ratio of these two variants in P. syringae B301D-R is 0.8, it is 0.2 in AP16 (Table 2); i.e., syringolin C has 4-fold-lower abundance in the latter strain. P. syringae SylC was experimentally shown to be the NRPS starter module to activate valine and, to a lesser extent, isoleucine and to form an ureidodipeptide, whereby the ureido carbonyl group is derived from hydrogen carbonate/carbon dioxide (15,16). In contrast to P. syringae, in AP16, valine is much less likely to be substituted by isoleucine at the ring-proximal position than at the distal position.…”

Section: Discussionmentioning

confidence: 99%

“…The sylC and sylD genes encode the NRPS/ PKS responsible for syringolin biosynthesis, whereas sylB encodes a desaturase thought to mediate the conversion of lysine to 3,4-dehydrolysine in the ring structure. Based on the sequence and architecture of the syl gene cluster, an experimentally supported biosynthesis model of syringolin A was proposed which explains all structural features of the molecule (13,(15)(16)(17)(18). The syringolin variants are the result of incomplete lysine desaturation by SylB and a relaxed specificity of the SylC NRPS module, which, in addition to valine, activates also isoleucine, although with reduced efficiency (3, 15).…”

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Production of Proteasome Inhibitor Syringolin A by the Endophyte Rhizobium sp. Strain AP16

Dudnik

Bigler

Dudler

2014

Appl Environ Microbiol

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bSyringolin A, the product of a mixed nonribosomal peptide synthetase/polyketide synthase encoded by the syl gene cluster, is a virulence factor secreted by certain Pseudomonas syringae strains. Together with the glidobactins produced by a number of betaand gammaproteobacterial human and animal pathogens, it belongs to the syrbactins, a structurally novel class of proteasome inhibitors. In plants, proteasome inhibition by syringolin A-producing P. syringae strains leads to the suppression of host defense pathways requiring proteasome activity, such as the ones mediated by salicylic acid and jasmonic acid. Here we report the discovery of a syl-like gene cluster with some unusual features in the alphaproteobacterial endophyte Rhizobium sp. strain AP16 that encodes a putative syringolin A-like synthetase whose components share 55% to 65% sequence identity (72% to 79% similarity) at the amino acid level. As revealed by average nucleotide identity (ANI) calculations, this strain likely belongs to the same species as biocontrol strain R. rhizogenes K84 (formely known as Agrobacterium radiobacter K84), which, however, carries a nonfunctional deletion remnant of the syl-like gene cluster. Here we present a functional analysis of the syl-like gene cluster of Rhizobium sp. strain AP16 and demonstrate that this endophyte synthesizes syringolin A and some related minor variants, suggesting that proteasome inhibition by syrbactin production can be important not only for pathogens but also for endophytic bacteria in the interaction with their hosts. Syringolin A was originally isolated from culture supernatants of the phytopathogenic gammaproteobacterium Pseudomonas syringae pv. syringae B301D-R based on its ability to elicit defense responses and pathogen resistance in rice plants (1, 2). It is a tripeptide derivative consisting an N-terminal valine and the two nonproteinogenic amino acids, 3,4-dehydrolysine and 5-methyl-4-amino-2-hexenoic acid; the first is N-acylated with an unusual ureido-valine moiety, and the latter two form a 12-member macrolactam ring (Fig. 1A). Syringolin A is the major variant of a family of related compounds in which one or both valine residues can be replaced by isoleucine and/or 3,4-dehydrolysine can be replaced by lysine (3). Syringolin A was shown to be a virulence factor in the interaction of P. syringae strain B728a with its host plant Phaseolus vulgaris (bean) where loss of syringolin A production resulted in a significantly diminished lesion number (4). The elucidation of the mode of action of syringolin A revealed that it irreversibly inhibited all three proteolytic activities (i.e., the caspase-, trypsin-, and chymotrypsin-like activities) of the eukaryotic proteasome by covalent ether bond formation with the active-site N-terminal threonine residues of the catalytic ␤1, ␤2, and ␤5 subunits of the 20S core proteasome (4). Proteasome inhibition suppresses the action of many plant hormones, including defense reactions mediated by the important defense hormones jasmonic acid (JA) and salicyl...

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Biosynthesis of the proteasome inhibitor syringolin A: the ureido group joining two amino acids originates from bicarbonate

Cited by 37 publications

References 38 publications

The role of bacterial phytotoxins in inhibiting the eukaryotic proteasome

The role of bacterial phytotoxins in inhibiting the eukaryotic proteasome

Proteasome Activity Imaging and Profiling Characterizes Bacterial Effector Syringolin A

Production of Proteasome Inhibitor Syringolin A by the Endophyte Rhizobium sp. Strain AP16

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