Family Of Lytic Polysaccharide Monooxygenases Research Articles

Advance in Heterologous Expression of Biomass-Degrading Auxiliary Activity 10 Family of Lytic Polysaccharide Monooxygenases

AA10 family lytic polysaccharide monooxygenases (AA10 LPMOs) are mainly distributed in bacteria. Because of their characteristics of oxidative degradation of crystalline polysaccharides, such as cellulose and chitin, they have great application potential in industrial biomass conversion and have attracted wide attention. Efficient heterologous expression of LPMOs by recombinant engineering bacteria has become the main strategy for the industrial production of enzymes. The research progress of AA10 LPMOs’ heterologous expression systems was reviewed in this paper. The construction strategies of its diversified heterologous expression system were introduced based on the design and processing of the expression host, vector, and LPMOs gene. The effects of different expression systems on the soluble expression of LPMOs and the development direction of the construction of LPMOs’ heterologous expression systems were discussed. The broad application prospect of LPMOs in the biomass conversion and biofuel industry has been prospected.

Revisiting the AA14 family of lytic polysaccharide monooxygenases and their catalytic activity.

Lytic polysaccharide monooxygenases (LPMOs) belonging to the AA14 family are believed to contribute to the enzymatic degradation of lignocellulosic biomass by specifically acting on xylan in recalcitrant cellulose-xylan complexes. Functional characterization of an AA14 LPMO from Trichoderma reesei, TrAA14A, and a re-evaluation of the properties of the previously described AA14 from Pycnoporus coccineus, PcoAA14A, showed that these proteins have oxidase and peroxidase activities that are common for LPMOs. However, we were not able to detect activity on cellulose-associated xylan or any other tested polysaccharide substrate, meaning that the substrate of these enzymes remains unknown. Next to raising questions regarding the true nature of AA14 LPMOs, the present data illustrate possible pitfalls in the functional characterization of these intriguing enzymes.

Decoding the Ambiguous Electron Paramagnetic Resonance Signals in the Lytic Polysaccharide Monooxygenase from Photorhabdus luminescens.

Understanding the structure and function of lytic polysaccharide monooxygenases (LPMOs), copper enzymes that degrade recalcitrant polysaccharides, requires the reliable atomistic interpretation of electron paramagnetic resonance (EPR) data on the Cu(II) active site. Among various LPMO families, the chitin-active PlAA10 shows an intriguing phenomenology with distinct EPR signals, a major rhombic and a minor axial signal. Here, we combine experimental and computational investigations to uncover the structural identity of these signals. X-band EPR spectra recorded at different pH values demonstrate pH-dependent population inversion: the major rhombic signal at pH 6.5 becomes minor at pH 8.5, where the axial signal dominates. This suggests that a protonation change is involved in the interconversion. Precise structural interpretations are pursued with quantum chemical calculations. Given that accurate calculations of Cu g-tensors remain challenging for quantum chemistry, we first address this problem via a thorough calibration study. This enables us to define a density functional that achieves accurate and reliable prediction of g-tensors, giving confidence in our evaluation of PlAA10 LPMO models. Large models were considered that include all parts of the protein matrix surrounding the Cu site, along with the characteristic second-sphere features of PlAA10. The results uniquely identify the rhombic signal with a five-coordinate Cu ion bearing two water molecules in addition to three N-donor ligands. The axial signal is attributed to a four-coordinate Cu ion where only one of the waters remains bound, as hydroxy. Alternatives that involve decoordination of the histidine brace amino group are unlikely based on energetics and spectroscopy. These results provide a reliable spectroscopy-consistent view on the plasticity of the resting state in PlAA10 LPMO as a foundation for further elucidating structure–property relationships and the formation of catalytically competent species. Our strategy is generally applicable to the study of EPR parameters of mononuclear copper-containing metalloenzymes.

A sensitive, accurate, and high-throughput gluco-oligosaccharide oxidase-based HRP colorimetric method for assaying lytic polysaccharide monooxygenase activity

BackgroundThe AA9 (auxiliary activities) family of lytic polysaccharide monooxygenases (AA9 LPMOs) is a ubiquitous and diverse group of enzymes in the fungal kingdom. They catalyse the oxidative cleavage of glycosidic bonds in lignocellulose and exhibit great potential for biorefinery applications. Robust, high-throughput and direct methods for assaying AA9 LPMO activity, which are prerequisites for screening LPMOs with excellent properties, are still lacking. Here, we present a gluco-oligosaccharide oxidase (GOOX)-based horseradish peroxidase (HRP) colorimetric method for assaying AA9 LPMO activity.ResultsWe cloned and expressed a GOOX gene from Sarocladium strictum in Trichoderma reesei, purified the recombinant SsGOOX, validated its properties, and developed an SsGOOX-based HRP colorimetric method for assaying cellobiose concentrations. Then, we expressed two AA9 LPMOs from Thielavia terrestris, TtAA9F and TtAA9G, in T. reesei, purified the recombinant proteins, and analysed their product profiles and regioselectivity towards phosphoric acid swollen cellulose (PASC). TtAA9F was characterized as a C1-type (class 1) LPMO, while TtAA9G was characterized as a C4-type (class 2) LPMO. Finally, the SsGOOX-based HRP colorimetric method was used to quantify the total concentration of reducing lytic products from the LPMO reaction, and the activities of both the C1- and C4-type LPMOs were analysed. These LPMOs could be effectively analysed with limits of detection (LoDs) less than 30 nmol/L, and standard curves between the A515 and LPMO concentrations with determination coefficients greater than 0.994 were obtained.ConclusionsA novel, sensitive and accurate assay method that directly targets the main activity of both C1- and C4-type AA9 LPMOs was established. This method is easy to use and could be performed on a microtiter plate for high-throughput screening of AA9 LPMOs with desirable properties.

Characterization of a lytic polysaccharide monooxygenase from Aspergillus fumigatus shows functional variation among family AA11 fungal LPMOs

The discovery of oxidative cleavage of recalcitrant polysaccharides by lytic polysaccharide monooxygenases (LPMOs) has affected the study and industrial application of enzymatic biomass processing. Despite being widespread in fungi, LPMOs belonging to the auxiliary activity (AA) family AA11 have been understudied. While these LPMOs are considered chitin active, some family members have little or no activity toward chitin, and the only available crystal structure of an AA11 LPMO lacks features found in bacterial chitin-active AA10 LPMOs. Here, we report structural and functional characteristics of a single-domain AA11 LPMO from Aspergillus fumigatus, AfAA11A. The crystal structure shows a substrate-binding surface with features resembling those of known chitin-active LPMOs. Indeed, despite the absence of a carbohydrate-binding module, AfAA11A has considerable affinity for α-chitin and, more so, β-chitin. AfAA11A is active toward both these chitin allomorphs and enhances chitin degradation by an endoacting chitinase, in particular for α-chitin. The catalytic activity of AfAA11A on chitin increases when supplying reactions with hydrogen peroxide, showing that, like LPMOs from other families, AfAA11A has peroxygenase activity. These results show that, in stark contrast to the previously characterized AfAA11B from the same organism, AfAA11A likely plays a role in fungal chitin turnover. Thus, members of the hitherto rather enigmatic family of AA11 LPMOs show considerable structural and functional differences and may have multiple roles in fungal physiology.

Bioinformatic Analysis of Lytic Polysaccharide Monooxygenases Reveals the Pan-Families Occurrence of Intrinsically Disordered C-Terminal Extensions.

Lytic polysaccharide monooxygenases (LPMOs) are monocopper enzymes secreted by many organisms and viruses. LPMOs catalyze the oxidative cleavage of different types of polysaccharides and are today divided into eight families (AA9–11, AA13–17) within the Auxiliary Activity enzyme class of the CAZy database. LPMOs minimal architecture encompasses a catalytic domain, to which can be appended a carbohydrate-binding module. Intriguingly, we observed that some LPMO sequences also display a C-terminal extension of varying length not associated with any known function or fold. Here, we analyzed 27,060 sequences from different LPMO families and show that 60% have a C-terminal extension predicted to be intrinsically disordered. Our analysis shows that these disordered C-terminal regions (dCTRs) are widespread in all LPMO families (except AA13) and differ in terms of sequence length and amino-acid composition. Noteworthily, these dCTRs have so far only been observed in LPMOs. LPMO-dCTRs share a common polyampholytic nature and an enrichment in serine and threonine residues, suggesting that they undergo post-translational modifications. Interestingly, dCTRs from AA11 and AA15 are enriched in redox-sensitive, conditionally disordered regions. The widespread occurrence of dCTRs in LPMOs from evolutionarily very divergent organisms, hints at a possible functional role and opens new prospects in the field of LPMOs.

Quantifying Oxidation of Cellulose-Associated Glucuronoxylan by Two Lytic Polysaccharide Monooxygenases from Neurospora crassa.

ABSTRACTFamily AA9 lytic polysaccharide monooxygenases (LPMOs) are abundant in fungi, where they catalyze oxidative depolymerization of recalcitrant plant biomass. These AA9 LPMOs cleave cellulose and some also act on hemicelluloses, primarily other (substituted) β-(1→4)-glucans. Oxidative cleavage of xylan has been shown for only a few AA9 LPMOs, and it remains unclear whether this activity is a minor side reaction or primary function. Here, we show that Neurospora crassa LPMO9F (NcLPMO9F) and the phylogenetically related, hitherto uncharacterized NcLPMO9L from N. crassa are active on both cellulose and cellulose-associated glucuronoxylan but not on glucuronoxylan alone. A newly developed method for simultaneous quantification of xylan-derived and cellulose-derived oxidized products showed that NcLPMO9F preferentially cleaves xylan when acting on a cellulose–beechwood glucuronoxylan mixture, yielding about three times more xylan-derived than cellulose-derived oxidized products. Interestingly, under similar conditions, NcLPMO9L and the previously characterized McLPMO9H, from Malbranchea cinnamomea, showed different xylan-to-cellulose preferences, giving oxidized product ratios of about 0.5:1 and 1:1, respectively, indicative of functional variation among xylan-active LPMOs. Phylogenetic and structural analysis of xylan-active AA9 LPMOs led to the identification of characteristic structural features, including unique features that do not occur in phylogenetically remote AA9 LPMOs, such as four AA9 LPMOs whose lack of activity toward glucuronoxylan was demonstrated in the present study. Taken together, the results provide a path toward discovery of additional xylan-active LPMOs and show that the huge family of AA9 LPMOs has members that preferentially act on xylan. These findings shed new light on the biological role and industrial potential of these fascinating enzymes.IMPORTANCE Plant cell wall polysaccharides are highly resilient to depolymerization by hydrolytic enzymes, partly due to cellulose chains being tightly packed in microfibrils that are covered by hemicelluloses. Lytic polysaccharide monooxygenases (LPMOs) seem well suited to attack these resilient copolymeric structures, but the occurrence and importance of hemicellulolytic activity among LPMOs remain unclear. Here, we show that certain AA9 LPMOs preferentially cleave xylan when acting on a cellulose–glucuronoxylan mixture, and that this ability is the result of protein evolution that has resulted in a clade of AA9 LPMOs with specific structural features. Our findings strengthen the notion that the vast arsenal of AA9 LPMOs in certain fungal species provides functional versatility and that AA9 LPMOs may have evolved to promote oxidative depolymerization of a wide variety of recalcitrant, copolymeric plant polysaccharide structures. These findings have implications for understanding the biological roles and industrial potential of LPMOs.

Potato pectin falls to Phytophthora

Plant Science P hytophthora infestans is a plant oomycete pathogen that drove the potato famines of the 1800s and continues to afflict potato fields today. The polysaccharide pectin makes up about a third of the cell wall in potatoes. Sabbadin et al. identified a family of lytic polysaccharide monooxygenases (LMPOs) that cleave pectin and are up-regulated in P. infestans during infection. Silencing the relevant LMPO gene successfully inhibited P. infestans infections. These findings open doors for disease intervention targets and for biotech applications. Science , abj1342, this issue p. [774][1] [1]: /lookup/doi/10.1126/science.abj1342

Secreted pectin monooxygenases drive plant infection by pathogenic oomycetes.

The oomycete Phytophthora infestans is a damaging crop pathogen and a model organism to study plant-pathogen interactions. We report the discovery of a family of copper-dependent lytic polysaccharide monooxygenases (LPMOs) in plant pathogenic oomycetes and its role in plant infection by P. infestans We show that LPMO-encoding genes are up-regulated early during infection and that the secreted enzymes oxidatively cleave the backbone of pectin, a charged polysaccharide in the plant cell wall. The crystal structure of the most abundant of these LPMOs sheds light on its ability to recognize and degrade pectin, and silencing the encoding gene in P. infestans inhibits infection of potato, indicating a role in host penetration. The identification of LPMOs as virulence factors in pathogenic oomycetes opens up opportunities in crop protection and food security.

Estimating the accuracy of calculated electron paramagnetic resonance hyperfine couplings for a lytic polysaccharide monooxygenase

Lytic polysaccharide monooxygenases (LPMOs) are enzymes that bind polysaccharides followed by an (oxidative) disruption of the polysaccharide surface, thereby boosting depolymerization. The binding process between the LPMO catalytic domain and polysaccharide is key to the mechanism and establishing structure-function relationships for this binding is therefore crucial. The hyperfine coupling constants (HFCs) from EPR spectroscopy have proven useful for this purpose. Unfortunately, EPR does not provide direct structural data and therefore the experimental EPR parameters have to be supported with parameters calculated with density functional theory. Yet, calculated HFCs are extremely sensitive to the employed computational setup. Using the LPMO Ls(AA9)A catalytic domain, we here quantify the importance of several choices in the computational setup, ranging from the use of specialized basis, the underlying structures, and the employed exchange-correlation functional. We show that specialized basis sets are an absolute necessity, and also that care has to be taken in the optimization of the underlying structure: only by allowing large parts of the protein around the active site to structurally relax could we obtain results that uniformly reproduced experimental trends. We compare our results to previously published X-ray structures and experimental HFCs for Ls(AA9)A as well as to recent experimental/theoretical results for another (AA10) family of LPMOs.

Do Lytic Polysaccharide Monooxygenases Aid in Plant Pathogenesis and Herbivory?

Lytic polysaccharide monooxygenases (LPMOs), copper-dependent enzymes mainly found in fungi, bacteria, and viruses, are responsible for enabling plant infection and degradation processes. Since their discovery 10 years ago, significant progress has been made in understanding the major role these enzymes play in biomass conversion. The recent discovery of additional LPMO families in fungi and oomycetes (AA16) as well as insects (AA15) strongly suggests that LPMOs might also be involved in biological processes such as overcoming plant defenses. In this review, we aim to give a comprehensive overview of the potential role of different LPMO families from the perspective of plant defense and their multiple implications in devising new strategies for achieving crop protection from plant pathogens and insect pests.

PreDSLpmo: A neural network-based prediction tool for functional annotation of lytic polysaccharide monooxygenases

Lytic polysaccharide monooxygenases (LPMOs), a family of copper-dependent oxidative enzymes, boost the degradation of polysaccharides such as cellulose, chitin, and others. While experimental methods are used to validate LPMO function, a computational method that can aid experimental methods and provide fast and accurate classification of sequences into LPMOs and its families would be an important step towards understanding the breadth of contributions these enzymes make in deconstruction of recalcitrant polysaccharides. In this study, we developed a machine learning-based tool called PreDSLpmo that employs two different approaches to functionally classify protein sequences into the major LPMO families (AA9 and AA10). The first approach uses a traditional neural network or multilayer percerptron-based approach, while the second employs bi-directional long short-term memory for sequence classification. Our method shows improvement in predictive power when compared with dbCAN2, an existing HMM-profile-based CAZyme predicting tool, on both validation and independent benchmark set.

Characterization of a novel Lytic Polysaccharide Monooxygenase from Malbranchea cinnamomea exhibiting dual catalytic behavior

A novel Lytic Polysaccharide Monooxygenase (LPMO) family AA9 (PMO9A_MALCI) protein from thermophilic fungus Malbranchea cinnamomea was cloned and expressed in Pichia pastoris. The expressed protein was purified to homogeneity using ion exchange and hydrophobic interaction chromatography. SDS-PAGE analysis showed PMO9A_MALCI to be ~27 kDa protein. High performance anion exchange chromatography and mass spectrometry confirmed that purified protein was active against an array of cellulosic (avicel, carboxy methyl cellulose) and hemicellulosic (birch wood xylan, wheat arabinoxylan and rye arabinoxylan) substrates, releasing both oxidized and unoxidized cello-oligosaccharide and xylo-oligosaccharide products respectively. Presence of double oxidized products during mass spectrometric analysis as well as in-silico analysis confirmed that the expressed protein belongs to Type 3 LPMO family. Molecular dynamic simulations further confirmed the sharing of common amino acid residues conserved for catalysis of both cellulosic and hemicellulosic substrates which further indicates that both substrates are equally preferred. Enzymatic cocktails constituted by replacing a part of commercial cellulase CellicCTec2 with PMO9A_MALCI (9:1/8:2) led to synergistic improvement in saccharification of acid and alkali pretreated biomass. This is the first report on heterologous expression of LPMO from M. cinnamomea, exhibiting catalysis of cellulose and pure xylan.

An ancient family of lytic polysaccharide monooxygenases with roles in arthropod development and biomass digestion

Thermobia domestica belongs to an ancient group of insects and has a remarkable ability to digest crystalline cellulose without microbial assistance. By investigating the digestive proteome of Thermobia, we have identified over 20 members of an uncharacterized family of lytic polysaccharide monooxygenases (LPMOs). We show that this LPMO family spans across several clades of the Tree of Life, is of ancient origin, and was recruited by early arthropods with possible roles in remodeling endogenous chitin scaffolds during development and metamorphosis. Based on our in-depth characterization of Thermobia’s LPMOs, we propose that diversification of these enzymes toward cellulose digestion might have endowed ancestral insects with an effective biochemical apparatus for biomass degradation, allowing the early colonization of land during the Paleozoic Era. The vital role of LPMOs in modern agricultural pests and disease vectors offers new opportunities to help tackle global challenges in food security and the control of infectious diseases.

High-resolution structure of a lytic polysaccharide monooxygenase from Hypocrea jecorina reveals a predicted linker as an integral part of the catalytic domain

For decades, the enzymes of the fungus Hypocrea jecorina have served as a model system for the breakdown of cellulose. Three-dimensional structures for almost all H. jecorina cellulose-degrading enzymes are available, except for HjLPMO9A, belonging to the AA9 family of lytic polysaccharide monooxygenases (LPMOs). These enzymes enhance the hydrolytic activity of cellulases and are essential for cost-efficient conversion of lignocellulosic biomass. Here, using structural and spectroscopic analyses, we found that native HjLPMO9A contains a catalytic domain and a family-1 carbohydrate-binding module (CBM1) connected via a linker sequence. A C terminally truncated variant of HjLPMO9A containing 21 residues of the predicted linker was expressed at levels sufficient for analysis. Here, using structural, spectroscopic, and biochemical analyses, we found that this truncated variant exhibited reduced binding to and activity on cellulose compared with the full-length enzyme. Importantly, a 0.95-Å resolution X-ray structure of truncated HjLPMO9A revealed that the linker forms an integral part of the catalytic domain structure, covering a hydrophobic patch on the catalytic AA9 module. We noted that the oxidized catalytic center contains a Cu(II) coordinated by two His ligands, one of which has a His-brace in which the His-1 terminal amine group also coordinates to a copper. The final equatorial position of the Cu(II) is occupied by a water-derived ligand. The spectroscopic characteristics of the truncated variant were not measurably different from those of full-length HjLPMO9A, indicating that the presence of the CBM1 module increases the affinity of HjLPMO9A for cellulose binding, but does not affect the active site.

The discovery of novel LPMO families with a new Hidden Markov model

BackgroundRenewable biopolymers, such as cellulose, starch and chitin are highly resistance to enzymatic degradation. Therefore, there is a need to upgrade current degradation processes by including novel enzymes. Lytic polysaccharide mono-oxygenases (LPMOs) can disrupt recalcitrant biopolymers, thereby enhancing hydrolysis by conventional enzymes. However, novel LPMO families are difficult to identify using existing methods. Therefore, we developed a novel profile Hidden Markov model (HMM) and used it to mine genomes of ascomycetous fungi for novel LPMOs.ResultsWe constructed a structural alignment and verified that the alignment was correct. In the alignment we identified several known conserved features, such as the histidine brace and the N/Q/E-X-F/Y motif and previously unidentified conserved proline and glycine residues. These residues are distal from the active site, suggesting a role in structure rather than activity. The multiple protein alignment was subsequently used to build a profile Hidden Markov model. This model was initially tested on manually curated datasets and proved to be both sensitive (no false negatives) and specific (no false positives). In some of the genomes analyzed we identified a yet unknown LPMO family. This new family is mostly confined to the phyla of Ascomycota and Basidiomycota and the class of Oomycota. Genomic clustering indicated that at least some members might be involved in the degradation of β-glucans, while transcriptomic data suggested that others are possibly involved in the degradation of pectin.ConclusionsThe newly developed profile hidden Markov Model was successfully used to mine fungal genomes for a novel family of LPMOs. However, the model is not limited to bacterial and fungal genomes. This is illustrated by the fact that the model was also able to identify another new LPMO family in Drosophila melanogaster. Furthermore, the Hidden Markov model was used to verify the more distant blast hits from the new fungal family of LPMOs, which belong to the Bivalves, Stony corals and Sea anemones. So this Hidden Markov model (Additional file 3) will help the broader scientific community in identifying other yet unknown LPMOs.

A family of AA9 lytic polysaccharide monooxygenases in Aspergillus nidulans is differentially regulated by multiple substrates and at least one is active on cellulose and xyloglucan.

Fungal genomes contain multiple genes encoding AA9 lytic polysaccharide monooxygenases (LPMOs), a recently discovered class of enzymes known to be active on cellulose and expressed when grown on biomass. Because of extensive genetic and biochemical data already available, Aspergillus nidulans offers an excellent model system to study the need for multiple AA9 LPMOs and their activity during oxidative degradation of biomass. We provide the first report on regulation of the entire family of AA9 LPMOs in A. nidulans over a range of polysaccharides including xylan, xyloglucan, pectin, glucan, and cellulose. We have successfully cloned and expressed AN3046, an AA9 LPMO in A. nidulans that is active on cellulose. Additionally, we performed mass spectral analyses that show the enzyme is active on the hemicellulose xyloglucan. The AN3046 LPMO showed synergy with other hydrolases in degrading sorghum stover. Our data showing activity of the overexpressed LPMO on cellulose and xyloglucan provides further evidence for the breadth of substrates acted on by AA9 LPMOs.

Evolution of substrate specificity in bacterial AA10 lytic polysaccharide monooxygenases.

BackgroundUnderstanding the diversity of lignocellulose-degrading enzymes in nature will provide insights for the improvement of cellulolytic enzyme cocktails used in the biofuels industry. Two families of enzymes, fungal AA9 and bacterial AA10, have recently been characterized as crystalline cellulose or chitin-cleaving lytic polysaccharide monooxygenases (LPMOs). Here we analyze the sequences, structures, and evolution of LPMOs to understand the factors that may influence substrate specificity both within and between these enzyme families.ResultsComparative analysis of sequences, solved structures, and homology models from AA9 and AA10 LPMO families demonstrated that, although these two LPMO families are highly conserved, structurally they have minimal sequence similarity outside the active site residues. Phylogenetic analysis of the AA10 family identified clades with putative chitinolytic and cellulolytic activities. Estimation of the rate of synonymous versus non-synonymous substitutions (dN/dS) within two major AA10 subclades showed distinct selective pressures between putative cellulolytic genes (subclade A) and CBP21-like chitinolytic genes (subclade D). Estimation of site-specific selection demonstrated that changes in the active sites were strongly negatively selected in all subclades. Furthermore, all codons in the subclade D had dN/dS values of less than 0.7, whereas codons in the cellulolytic subclade had dN/dS values of greater than 1.5. Positively selected codons were enriched at sites localized on the surface of the protein adjacent to the active site.ConclusionsThe structural similarity but absence of significant sequence similarity between AA9 and AA10 families suggests that these enzyme families share an ancient ancestral protein. Combined analysis of amino acid sites under Darwinian selection and structural homology modeling identified a subclade of AA10 with diversifying selection at different surfaces, potentially used for cellulose-binding and protein-protein interactions. Together, these data indicate that AA10 LPMOs are under selection to change their function, which may optimize cellulolytic activity. This work provides a phylogenetic basis for identifying and classifying additional cellulolytic or chitinolytic LPMOs.Electronic supplementary materialThe online version of this article (doi:10.1186/1754-6834-7-109) contains supplementary material, which is available to authorized users.

Paenibacillus larvae chitin-degrading protein PlCBP49 is a key virulence factor in American Foulbrood of honey bees.

Paenibacillus larvae, the etiological agent of the globally occurring epizootic American Foulbrood (AFB) of honey bees, causes intestinal infections in honey bee larvae which develop into systemic infections inevitably leading to larval death. Massive brood mortality might eventually lead to collapse of the entire colony. Molecular mechanisms of host-microbe interactions in this system and of differences in virulence between P. larvae genotypes are poorly understood. Recently, it was demonstrated that the degradation of the peritrophic matrix lining the midgut epithelium is a key step in pathogenesis of P. larvae infections. Here, we present the isolation and identification of PlCBP49, a modular, chitin-degrading protein of P. larvae and demonstrate that this enzyme is crucial for the degradation of the larval peritrophic matrix during infection. PlCBP49 contains a module belonging to the auxiliary activity 10 (AA10, formerly CBM33) family of lytic polysaccharide monooxygenases (LPMOs) which are able to degrade recalcitrant polysaccharides. Using chitin-affinity purified PlCBP49, we provide evidence that PlCBP49 degrades chitin via a metal ion-dependent, oxidative mechanism, as already described for members of the AA10 family. Using P. larvae mutants lacking PlCBP49 expression, we analyzed in vivo biological functions of PlCBP49. In the absence of PlCBP49 expression, peritrophic matrix degradation was markedly reduced and P. larvae virulence was nearly abolished. This indicated that PlCBP49 is a key virulence factor for the species P. larvae. The identification of the functional role of PlCBP49 in AFB pathogenesis broadens our understanding of this important family of chitin-binding and -degrading proteins, especially in those bacteria that can also act as entomopathogens.

Discovery and characterization of a new family of lytic polysaccharide monooxygenases

Lytic polysaccharide mono-oxygenases (LPMOs) are a recently discovered class of enzymes capable of oxidizing recalcitrant polysaccharides. They currently attract much attention due to their potential use in biomass conversion, notably in the production of biofuels. Past work has identified two discrete sequence-based families of these enzymes termed AA9 (formerly GH61) and AA10 (formerly CBM33). Here we report the discovery of a third family of LPMOs. Using a chitin-degrading exemplar from Aspergillus oryzae, we show that the 3-D structure of the enzyme shares some features of the previous two classes of LPMOs, including a copper active centre featuring the histidine brace active site, but is distinct in terms of its active site details and its EPR spectroscopy. The new AA11 family expands the LPMO clan with the potential to broaden both the range of potential substrates and the types of reactive copper-oxygen species formed at the active site of LPMOs.