Mononuclear molybdoenzymes are highly versatile catalysts that occur in organisms in all domains of life, where they mediate essential cellular functions such as energy generation and detoxification ...reactions. Molybdoenzymes are particularly abundant in bacteria, where over 50 distinct types of enzymes have been identified to date. In bacterial pathogens, all aspects of molybdoenzyme biology such as molybdate uptake, cofactor biosynthesis, and function of the enzymes themselves, have been shown to affect fitness in the host as well as virulence. Although current studies are mostly focused on a few key pathogens such as
, and
, some common themes for the function and adaptation of the molybdoenzymes to pathogen environmental niches are emerging. Firstly, for many of these enzymes, their role is in supporting bacterial energy generation; and the corresponding pathogen fitness and virulence defects appear to arise from a suboptimally poised metabolic network. Secondly, all substrates converted by virulence-relevant bacterial Mo enzymes belong to classes known to be generated in the host either during inflammation or as part of the host signaling network, with some enzyme groups showing adaptation to the increased conversion of such substrates. Lastly, a specific adaptation to bacterial in-host survival is an emerging link between the regulation of molybdoenzyme expression in bacterial pathogens and the presence of immune system-generated reactive oxygen species. The prevalence of molybdoenzymes in key bacterial pathogens including ESKAPE pathogens, paired with the mounting evidence of their central roles in bacterial fitness during infection, suggest that they could be important future drug targets.
The Toll/interleukin-1 receptor/resistance protein (TIR) domain is a protein–protein interaction domain consisting of 125–200 residues, widely distributed in animals, plants and bacteria but absent ...from fungi, archea and viruses. In plants and animals, these domains are found in proteins with functions in innate immune pathways, while in bacteria, some TIR domain-containing proteins interfere with the innate immune pathways in the host. TIR domains function as protein scaffolds, mostly involving self-association and homotypic interactions with other TIR domains. In the last 15 years, the three-dimensional structures of TIR domains from several mammalian, plant and bacterial proteins have been reported. These structures, jointly with functional data including the identification of interacting proteins, have started to provide insight into the molecular basis of the assembly of animal and plant immune signaling complexes, and for host immunosuppression by bacterial pathogens. This review focuses on the current knowledge of the structures of the TIR domains and how the structure relates to function.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Bacterial heterodimeric tryptophan-containing diketopiperazines (HTDKPs) are a growing family of bioactive natural products. They are challenging to prepare by chemical routes due to the polycyclic ...and densely functionalized backbone. Through functional characterization and investigation, we herein identify a family of three related HTDKP-forming cytochrome P450s (NasbB, Nas
and Nas
) and reveal four critical residues (Qln65, Ala86, Ser284 and Val288) that control their regio- and stereo-selectivity to generate diverse dimeric DKP frameworks. Engineering these residues can alter the specificities of the enzymes to produce diverse frameworks. Determining the crystal structures (1.70-1.47 Å) of Nas
(ligand-free and substrate-bound Nas
and its Q65I-A86G and S284A-V288A mutants) and molecular dynamics simulation finally elucidate the specificity-conferring mechanism of these residues. Our results provide a clear molecular and mechanistic basis into this family of HTDKP-forming P450s, laying a solid foundation for rapid access to the molecular diversity of HTDKP frameworks through rational engineering of the P450s.
SARM1 (sterile alpha and TIR motif containing 1) is responsible for depletion of nicotinamide adenine dinucleotide in its oxidized form (NAD
) during Wallerian degeneration associated with ...neuropathies. Plant nucleotide-binding leucine-rich repeat (NLR) immune receptors recognize pathogen effector proteins and trigger localized cell death to restrict pathogen infection. Both processes depend on closely related Toll/interleukin-1 receptor (TIR) domains in these proteins, which, as we show, feature self-association-dependent NAD
cleavage activity associated with cell death signaling. We further show that SARM1 SAM (sterile alpha motif) domains form an octamer essential for axon degeneration that contributes to TIR domain enzymatic activity. The crystal structures of ribose and NADP
(the oxidized form of nicotinamide adenine dinucleotide phosphate) complexes of SARM1 and plant NLR RUN1 TIR domains, respectively, reveal a conserved substrate binding site. NAD
cleavage by TIR domains is therefore a conserved feature of animal and plant cell death signaling pathways.
Animals and plants have NLRs (nucleotide-binding leucine-rich repeat receptors) that recognize the presence of pathogens and initiate innate immune responses. In plants, there are three types of NLRs ...distinguished by their N-terminal domain: the CC (coiled-coil) domain NLRs, the TIR (Toll/interleukin-1 receptor) domain NLRs and the RPW8 (resistance to powdery mildew 8)-like coiled-coil domain NLRs. CC-NLRs (CNLs) and TIR-NLRs (TNLs) generally act as sensors of effectors secreted by pathogens, while RPW8-NLRs (RNLs) signal downstream of many sensor NLRs and are called helper NLRs. Recent studies have revealed three dimensional structures of a CNL (ZAR1) including its inactive, intermediate and active oligomeric state, as well as TNLs (RPP1 and ROQ1) in their active oligomeric states. Furthermore, accumulating evidence suggests that members of the family of lipase-like EDS1 (enhanced disease susceptibility 1) proteins, which are uniquely found in seed plants, play a key role in providing a link between sensor NLRs and helper NLRs during innate immune responses. Here, we summarize the implications of the plant NLR structures that provide insights into distinct mechanisms of action by the different sensor NLRs and discuss plant NLR-mediated innate immune signalling pathways involving the EDS1 family proteins and RNLs.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Plant NLRs share many of the structural hallmarks of their animal counterparts. At a functional level, the central nucleotide-binding pocket appears to have binding and hydrolysis activities, similar ...to that of animal NLRs. The TIR domains of plant NLRs have been shown to self-associate, and there is emerging evidence that full-length plant NLRs may do so as well. It is therefore tempting to speculate that plant NLRs may form higher-order complexes similar to those of the mammalian inflammasome. Here we review the available knowledge on structure-function relationships in plant NLRs, focusing on how the information available on animal NLRs informs the mechanism of plant NLR function, and highlight the evidence that innate immunity signalling pathways in multicellular organisms often require the formation of higher-order protein complexes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Pattern recognition receptors (PRRs) of the mammalian innate immune system mediate the first line of defense against pathogens and danger signals.•PRRs signal via oligomeric signaling complexes that ...assemble via co-operative assembly mechanisms.•Signaling by co-operative assembly formation (SCAF) allows PRRs to respond rapidly and amplify the response to a low level of stimulus.•The molecular mechanisms of SCAF by NLR, PYHIN family, TLR and RIG-I receptors are reviewed.•Conservation of SCAF in plants and fungi is discussed.
The innate immune system is the first line of defense against infection and responses are initiated by pattern recognition receptors (PRRs) that detect pathogen-associated molecular patterns (PAMPs). PRRs also detect endogenous danger-associated molecular patterns (DAMPs) that are released by damaged or dying cells. The major PRRs include the Toll-like receptor (TLR) family members, the nucleotide binding and oligomerization domain, leucine-rich repeat containing (NLR) family, the PYHIN (ALR) family, the RIG-1-like receptors (RLRs), C-type lectin receptors (CLRs) and the oligoadenylate synthase (OAS)-like receptors and the related protein cyclic GMP-AMP synthase (cGAS). The different PRRs activate specific signaling pathways to collectively elicit responses including the induction of cytokine expression, processing of pro-inflammatory cytokines and cell-death responses. These responses control a pathogenic infection, initiate tissue repair and stimulate the adaptive immune system. A central theme of many innate immune signaling pathways is the clustering of activated PRRs followed by sequential recruitment and oligomerization of adaptors and downstream effector enzymes, to form higher-order arrangements that amplify the response and provide a scaffold for proximity-induced activation of the effector enzymes. Underlying the formation of these complexes are co-operative assembly mechanisms, whereby association of preceding components increases the affinity for downstream components. This ensures a rapid immune response to a low-level stimulus. Structural and biochemical studies have given key insights into the assembly of these complexes. Here we review the current understanding of assembly of immune signaling complexes, including inflammasomes initiated by NLR and PYHIN receptors, the myddosomes initiated by TLRs, and the MAVS CARD filament initiated by RIG-1. We highlight the co-operative assembly mechanisms during assembly of each of these complexes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Towards the structure of the TIR-domain signalosome Nimma, Surekha; Ve, Thomas; Williams, Simon J. ...
Current opinion in structural biology,
April 2017, 2017-Apr, 2017-04-00, 20170401, Volume:
43
Journal Article
Peer reviewed
Open access
•TIR domains feature in proteins associated with innate immunity in animals, plants and bacteria.•30 structures of 16 different TIR domains from animals, plants and bacteria are available.•Key to ...their function is self-association and homotypic association with other TIR domains.•Proposed models of how these domains associate and function have not agreed.•Signaling by cooperative assembly formation (SCAF) is proposed as the common mechanism of function.
TIR (Toll/interleukin-1 receptor/resistance protein) domains feature in animal, plant and bacterial proteins involved in innate immunity pathways and associated processes. They function through protein:protein interactions, in particular self-association and homotypic association with other TIR domains. Structures of TIR domains from all phyla have been determined, but common association modes have only emerged for plant and bacterial TIR domains, and not for mammalian TIR domains. Numerous attempts involving hybrid approaches, which have combined structural, computational, mutagenesis and biophysical data, have failed to converge onto common models of how these domains associate and function. We propose that the available data can be reconciled in the context of higher-order assembly formation, and that TIR domains function through signaling by cooperative assembly formation (SCAF).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Summary
Recent studies have identified that proteinaceous effectors secreted by Parastagonospora nodorum are required to cause disease on wheat. These effectors interact in a gene‐for‐gene manner ...with host‐dominant susceptibilty loci, resulting in disease. However, whilst the requirement of these effectors for infection is clear, their mechanisms of action remain poorly understood. A yeast‐two‐hybrid library approach was used to search for wheat proteins that interacted with the necrotrophic effector SnTox3. Using this strategy we indentified an interaction between SnTox3 and the wheat pathogenicity‐related protein TaPR‐1‐1, and confirmed it by in‐planta co‐immunprecipitation. PR‐1 proteins represent a large family (23 in wheat) of proteins that are upregulated early in the defence response; however, their function remains ellusive. Interestingly, the P. nodorum effector SnToxA has recently been shown to interact specifically with TaPR‐1‐5. Our analysis of the SnTox3–TaPR‐1 interaction demonstrated that SnTox3 can interact with a broader range of TaPR‐1 proteins. Based on these data we utilised homology modeling to predict, and validate, regions on TaPR‐1 proteins that are likely to be involved in the SnTox3 interaction. Precipitating from this work, we identified that a PR‐1‐derived defence signalling peptide from the C‐terminus of TaPR‐1‐1, known as CAPE1, enhanced the infection of wheat by P. nodorum in an SnTox3‐dependent manner, but played no role in ToxA‐mediated disease. Collectively, our data suggest that P. nodorum has evolved unique effectors that target a common host‐protein involved in host defence, albeit with different mechanisms and potentially outcomes.
Significance Statement
The mechanisms or modes‐of‐action of necrotrophic effector proteins in facilitating plant diseases are largely unknown. This report provides evidence that these critical pathogen proteins interact with the important, yet poorly understood, wheat PR‐1 proteins. The discovery that two independent pathogen effector proteins both target PR‐1 proteins strongly implicates a role for this protein interaction in facilitating disease.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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