Capture-and-release of a sulfoquinovose-binding protein on sulfoquinovose-modified agarose

The solute-binding protein (SBP) components of periplasmic binding protein-dependent ATP-binding cassette (ABC)-type transporters often possess exquisite selectivity for their cognate ligands. Maltose binding protein (MBP), the best studied of these SBPs, has been extensively used as a fusion partner to enable the affinity purification of recombinant proteins. However, other SBPs and SBP-ligand based affinity systems remain underexplored. The sulfoquinovose-binding protein SmoF, is a substrate-binding protein component of the ABC transporter cassette in Agrobacterium tumefaciens involved in importing sulfoquinovose (SQ) and its derivatives for SQ catabolism. Here, we show that SmoF binds with high affinity to the octyl glycoside of SQ (octyl-SQ), demonstrating remarkable tolerance to extension of the anomeric substituent. The 3D X-ray structure of the SmoF·octyl-SQ complex reveals accommodation of the octyl chain, which projects to the protein surface, providing impetus for the synthesis of a linker-equipped SQ-amine using a thiol-ene reaction as a key step, and its conjugation to cyanogen bromide modified agarose. We demonstrate the successful capture and release of SmoF from SQ-agarose resin using SQ as competitive eluant, and selectivity for release versus other organosulfonates. We show that SmoF can be captured and purified from a cell lysate, demonstrating the utility of SQ-agarose in capturing SQ binding proteins from complex mixtures. The present work provides a pathway for development of 'capture-and-release' affinity resins for the discovery and study of SBPs.

A Broad-Spectrum α-Glucosidase of Glycoside Hydrolase Family 13 from Marinovum sp., a Member of the Roseobacter Clade

Glycoside hydrolases (GHs) are a diverse group of enzymes that catalyze the hydrolysis of glycosidic bonds. The Carbohydrate-Active enZymes (CAZy) classification organizes GHs into families based on sequence data and function, with fewer than 1% of the predicted proteins characterized biochemically. Consideration of genomic context can provide clues to infer possible enzyme activities for proteins of unknown function. We used the MultiGeneBLAST tool to discover a gene cluster in Marinovum sp., a member of the marine Roseobacter clade, that encodes homologues of enzymes belonging to the sulfoquinovose monooxygenase pathway for sulfosugar catabolism. This cluster lacks a gene encoding a classical family GH31 sulfoquinovosidase candidate, but which instead includes an uncharacterized family GH13 protein (MsGH13) that we hypothesized could be a non-classical sulfoquinovosidase. Surprisingly, recombinant MsGH13 lacks sulfoquinovosidase activity and is a broad-spectrum α-glucosidase that is active on a diverse array of α-linked disaccharides, including maltose, sucrose, nigerose, trehalose, isomaltose, and kojibiose. Using AlphaFold, a 3D model for the MsGH13 enzyme was constructed that predicted its active site shared close similarity with an α-glucosidase from Halomonas sp. H11 of the same GH13 subfamily that shows narrower substrate specificity.

Correction: Molecular basis of sulfolactate synthesis by sulfolactaldehyde dehydrogenase from Rhizobium leguminosarum

[This corrects the article DOI: 10.1039/D3SC01594G.].

Widespread Family of NAD+-Dependent Sulfoquinovosidases at the Gateway to Sulfoquinovose Catabolism

The sulfosugar sulfoquinovose (SQ) is produced by photosynthetic plants, algae, and cyanobacteria on a scale of 10 billion tons per annum. Its degradation, which is essential to allow cycling of its constituent carbon and sulfur, involves specialized glycosidases termed sulfoquinovosidases (SQases), which release SQ from sulfolipid glycoconjugates, so SQ can enter catabolism pathways. However, many SQ catabolic gene clusters lack a gene encoding a classical SQase. Here, we report the discovery of a new family of SQases that use an atypical oxidoreductive mechanism involving NAD+ as a catalytic cofactor. Three-dimensional X-ray structures of complexes with SQ and NAD+ provide insight into the catalytic mechanism, which involves transient oxidation at C3. Bioinformatic survey reveals this new family of NAD+-dependent SQases occurs within sulfoglycolytic and sulfolytic gene clusters that lack classical SQases and is distributed widely including within Roseobacter clade bacteria, suggesting an important contribution to marine sulfur cycling.

Defining the molecular architecture, metal dependence, and distribution of metal-dependent class II sulfofructose-1-phosphate aldolases

Sulfoquinovose (SQ, 6-deoxy-6-sulfoglucose) is a sulfosugar that is the anionic head group of plant, algal, and cyanobacterial sulfolipids: sulfoquinovosyl diacylglycerols. SQ is produced within photosynthetic tissues, forms a major terrestrial reservoir of biosulfur, and is an important species within the biogeochemical sulfur cycle. A major pathway for SQ breakdown is the sulfoglycolytic Embden-Meyerhof-Parnas pathway, which involves cleavage of the 6-carbon chain of the intermediate sulfofructose-1-phosphate (SFP) into dihydroxyacetone and sulfolactaldehyde, catalyzed by class I or II SFP aldolases. While the molecular basis of catalysis is understood for class I SFP aldolases, comparatively little is known about class II SFP aldolases. Here, we report the molecular architecture and biochemical basis of catalysis of two metal-dependent class II SFP aldolases from Hafnia paralvei and Yersinia aldovae. 3D X-ray structures of complexes with substrate SFP and product dihydroxyacetone phosphate reveal a dimer-of-dimers (tetrameric) assembly, the sulfonate-binding pocket, two metal-binding sites, and flexible loops that are implicated in catalysis. Both enzymes were metal-dependent and exhibited high KM values for SFP, consistent with their role in a unidirectional nutrient acquisition pathway. Bioinformatic analysis identified a range of sulfoglycolytic Embden-Meyerhof-Parnas gene clusters containing class I/II SFP aldolases. The class I and II SFP aldolases have mututally exclusive occurrence within Actinobacteria and Firmicutes phyla, respectively, while both classes of enzyme occur within Proteobacteria. This work emphasizes the importance of SQ as a nutrient for diverse bacterial phyla and the different chemical strategies they use to harvest carbon from this sulfosugar.

The mycobacterial glycoside hydrolase LamH enables capsular arabinomannan release and stimulates growth

Mycobacterial glycolipids are important cell envelope structures that drive host-pathogen interactions. Arguably, the most important amongst these are lipoarabinomannan (LAM) and its precursor, lipomannan (LM), which are both trafficked out of the bacterium to the host via unknown mechanisms. An important class of exported LM/LAM is the capsular derivative of these molecules which is devoid of its lipid anchor. Here, we describe the identification of a glycoside hydrolase family 76 enzyme that we term LamH which specifically cleaves α-1,6-mannoside linkages within LM and LAM, driving its export to the capsule releasing its phosphatidyl-myo-inositol mannoside lipid anchor. Unexpectedly, we found that the catalytic activity of this enzyme is important for efficient exit from stationary phase cultures where arabinomannan acts as a signal for growth phase transition. Finally, we demonstrate that LamH is important for Mycobacterium tuberculosis survival in macrophages. These data provide a new framework for understanding the biological role of LAM in mycobacteria.

Molecular basis of sulfolactate synthesis by sulfolactaldehyde dehydrogenase from Rhizobium leguminosarum

Sulfolactate (SL) is a short-chain organosulfonate that is an important reservoir of sulfur in the biosphere. SL is produced by oxidation of sulfolactaldehyde (SLA), which in turn derives from sulfoglycolysis of the sulfosugar sulfoquinovose, or through oxidation of 2,3-dihydroxypropanesulfonate. Oxidation of SLA is catalyzed by SLA dehydrogenases belonging to the aldehyde dehydrogenase superfamily. We report that SLA dehydrogenase RlGabD from the sulfoglycolytic bacterium Rhizobium leguminsarum SRDI565 can use both NAD+ and NADP+ as cofactor to oxidize SLA, and indicatively operates through a rapid equilibrium ordered mechanism. We report the cryo-EM structure of RlGabD bound to NADH, revealing a tetrameric quaternary structure and supporting proposal of organosulfonate binding residues in the active site, and a catalytic mechanism. Sequence based homology searches identified SLA dehydrogenase homologs in a range of putative sulfoglycolytic gene clusters in bacteria predominantly from the phyla Actinobacteria, Firmicutes, and Proteobacteria. This work provides a structural and biochemical view of SLA dehydrogenases to complement our knowledge of SLA reductases, and provide detailed insights into a critical step in the organosulfur cycle.

Discovery and Biosynthesis of the Cytotoxic Polyene Terpenomycin in Human Pathogenic Nocardia

Nocardia are opportunistic human pathogens that can cause a range of debilitating and difficult to treat infections of the lungs, brain, skin, and soft tissues. Despite their close relationship to the well-known secondary metabolite-producing genus, Streptomyces, comparatively few natural products are known from the Nocardia, and even less is known about their involvement in the pathogenesis. Here, we combine chemistry, genomics, and molecular microbiology to reveal the production of terpenomycin, a new cytotoxic and antifungal polyene from a human pathogenic Nocardia terpenica isolate. We unveil the polyketide synthase (PKS) responsible for terpenomycin biosynthesis and show that it combines several unusual features, including "split", skipped, and iteratively used modules, and the use of the unusual extender unit methoxymalonate as a starter unit. To link genes to molecules, we constructed a transposon mutant library in N. terpenica, identifying a terpenomycin-null mutant with an inactivated terpenomycin PKS. Our findings show that the neglected actinomycetes have an unappreciated capacity for the production of bioactive molecules with unique biosynthetic pathways waiting to be uncovered and highlights these organisms as producers of diverse natural products.

Glycolipids from the gut symbiont Bacteroides fragilis are agonists for natural killer T cells and induce their regulatory differentiation

Natural Killer T (NKT) cells are a lipid-antigen reactive T cell subset that is restricted to the antigen presenting molecule CD1d. They possess diverse functional properties that contribute to inflammatory and regulatory immune responses. The most studied lipid antigen target for these T cells is α-galactosylceramide (αGC). The commensal organism Bacteroides fragilis (B. fragilis) produces several forms of αGC, but conflicting information exists about the influence of these lipids on NKT cells. Herein, we report the total synthesis of a major form of αGC from B. fragilis (Bf αGC), and several analogues thereof. We confirm the T cell receptor (TCR)-mediated recognition of these glycolipids by mouse and human NKT cells. Despite the natural structure of Bf αGC containing lipid branching that limits potency, we demonstrate that Bf αGC drives mouse NKT cells to proliferate and differentiate into producers of the immunoregulatory cytokine, interleukin-10 (IL-10). These Bf αGC-experienced NKT cells display regulatory function by inhibiting the expansion of naïve NKT cells upon subsequent exposure to this antigen. Moreover, this regulatory activity impacts more than just NKT cells, as demonstrated by the NKT cell-mediated inhibition of antigen-stimulated mucosal-associated invariant T (MAIT) cells (a T cell subset restricted to a different antigen presenting molecule, MR1). These findings reveal that B. fragilis-derived NKT cell agonists may have broad immunoregulatory activity, providing insight into the mechanisms influencing immune tolerance to commensal bacteria and highlighting a potential means to manipulate NKT cell function for therapeutic benefit.

Identification of D-arabinan-degrading enzymes in mycobacteria

Bacterial cell growth and division require the coordinated action of enzymes that synthesize and degrade cell wall polymers. Here, we identify enzymes that cleave the D-arabinan core of arabinogalactan, an unusual component of the cell wall of Mycobacterium tuberculosis and other mycobacteria. We screened 14 human gut-derived Bacteroidetes for arabinogalactan-degrading activities and identified four families of glycoside hydrolases with activity against the D-arabinan or D-galactan components of arabinogalactan. Using one of these isolates with exo-D-galactofuranosidase activity, we generated enriched D-arabinan and used it to identify a strain of Dysgonomonas gadei as a D-arabinan degrader. This enabled the discovery of endo- and exo-acting enzymes that cleave D-arabinan, including members of the DUF2961 family (GH172) and a family of glycoside hydrolases (DUF4185/GH183) that display endo-D-arabinofuranase activity and are conserved in mycobacteria and other microbes. Mycobacterial genomes encode two conserved endo-D-arabinanases with different preferences for the D-arabinan-containing cell wall components arabinogalactan and lipoarabinomannan, suggesting they are important for cell wall modification and/or degradation. The discovery of these enzymes will support future studies into the structure and function of the mycobacterial cell wall.

Identification of levoglucosan degradation pathways in bacteria and sequence similarity network analysis

Levoglucosan is produced in the pyrolysis of cellulose and starch, including from bushfires or the burning of biofuels, and is deposited from the atmosphere across the surface of the earth. We describe two levoglucosan degrading Paenarthrobacter spp. (Paenarthrobacter nitrojuajacolis LG01 and Paenarthrobacter histidinolovorans LG02) that were isolated from soil by metabolic enrichment using levoglucosan as the sole carbon source. Genome sequencing and proteomics analysis revealed the expression of a series of genes encoding known levoglucosan degrading enzymes, levoglucosan dehydrogenase (LGDH, LgdA), 3-keto-levoglucosan β -eliminase (LgdB1) and glucose 3-dehydrogenase (LgdC), along with an ABC transporter cassette and an associated solute binding protein. However, no homologues of 3-ketoglucose dehydratase (LgdB2) were evident, while the expressed genes contained a range of putative sugar phosphate isomerases/xylose isomerases with weak similarity to LgdB2. Sequence similarity network analysis of genome neighbours of LgdA revealed that homologues of LgdB1 and LgdC are generally conserved in a range of bacteria in the phyla Firmicutes, Actinobacteria and Proteobacteria. One group of sugar phosphate isomerase/xylose isomerase homologues (named LgdB3) was identified with limited distribution that is mutually exclusive with LgdB2, and we propose that they may fulfil a similar function. LgdB1, LgdB2 and LgdB3 adopt similar predicted 3D folds, suggesting overlapping function in processing intermediates in LG metabolism. Our findings highlight diversity within the LGDH pathway, through which bacteria utilize levoglucosan as a nutrient source.

A subfamily classification to choreograph the diverse activities within glycoside hydrolase family 31

The Carbohydrate-Active Enzyme classification groups enzymes that breakdown, assemble, or decorate glycans into protein families based on sequence similarity. The glycoside hydrolases (GH) are arranged into over 170 enzyme families, with some being very large and exhibiting distinct activities/specificities towards diverse substrates. Family GH31 is a large family that contains more than 20,000 sequences with a wide taxonomic diversity. Less than 1% of GH31 members are biochemically characterized and exhibit many different activities that include glycosidases, lyases, and transglycosidases. This diversity of activities limits our ability to predict the activities and roles of GH31 family members in their host organism and our ability to exploit these enzymes for practical purposes. Here, we established a subfamily classification using sequence similarity networks that was further validated by a structural analysis. While sequence similarity networks provide a sequence-based separation, we obtained good segregation between activities among the subfamilies. Our subclassification consists of 20 subfamilies with sixteen subfamilies containing at least one characterized member and eleven subfamilies that are monofunctional based on the available data. We also report the biochemical characterization of a member of the large subfamily 2 (GH31_2) that lacked any characterized members: RaGH31 from Rhodoferax aquaticus is an α-glucosidase with activity on a range of disaccharides including sucrose, trehalose, maltose, and nigerose. Our subclassification provides improved predictive power for the vast majority of uncharacterized proteins in family GH31 and highlights the remaining sequence space that remains to be functionally explored.

Synthesis and structure of clozapine N-oxide hemi(hydrochloride): an infinite hydrogen-bonded poly[n]catenane

The recrystallization of clozapine N-oxide hydro­chloride from a range of solvents leads to the loss of half an equivalent of HCl and the formation of single crystals of a hydrogen-bond-linked poly[n]catenane of clozapine N-oxide hemi­hydro­chloride.

The structure of the title compound, 2C₁₈H₁₉ClN₄O·HCl or (CNO)₂·HCl (C₃₆H₃₉Cl₃N₈O₂), at 100 K has tetra­gonal (I4/m) symmetry. The dihedral angle between the benzene rings of the fused ring system of the CNO mol­ecule is 40.08 (6)° and the equivalent angle between the seven-membered ring and its pendant N-oxide ring is 31.14 (7)°. The structure contains a very strong, symmetrical O—H⋯O hydrogen bond [O⋯O = 2.434 (2) Å] between two equivalent R₃N⁺—O⁻ moieties, which share a proton lying on a crystallographic twofold rotation axis. These units then form a (CNO)₄·(HCl)₂ ring by way of two equivalent N—H⋯Cl hydrogen bonds (Cl⁻ site symmetry m). These rings are catenated into infinite chains propagating along the c-axis direction by way of shape complementarity and directional C—H⋯N and C—H⋯π inter­actions.

Chemistry and biology of the aminosulfonate cysteinolic acid: discovery, distribution, synthesis and metabolism

D-Cysteinolic acid is a zwitterionic aminosulfonate found in marine (and occasionally freshwater) environments. It is distributed in a wide range of algae (red, green and brown algae and diatoms), and some bacteria and sea animals. It was discovered in 1957 and in spite of its long history, its biosynthesis and degradation is poorly understood. Cysteinolic acid is found conjugated to steroids, lipids and arsenosugars, and the cysteinolic acid motif is found within the structures of various capnoid and sulfoceramide sulfonolipids. This review provides an historical account of the discovery of D-cysteinolic acid and related molecules, its distribution and occurrence within marine and freshwater organisms, routes for its chemical synthesis, and summarizes knowledge and speculations surrounding its biosynthesis, degradation and bioconversions.

Genome sequences of Arthrobacter spp. that use a modified sulfoglycolytic Embden-Meyerhof-Parnas pathway

Sulfoglycolysis pathways enable the breakdown of the sulfosugar sulfoquinovose and environmental recycling of its carbon and sulfur content. The prototypical sulfoglycolytic pathway is a variant of the classical Embden–Meyerhof–Parnas (EMP) pathway that results in formation of 2,3-dihydroxypropanesulfonate and was first described in gram-negative Escherichia coli. We used enrichment cultures to discover new sulfoglycolytic bacteria from Australian soil samples. Two gram-positive Arthrobacter spp. were isolated that produced sulfolactate as the metabolic end-product. Genome sequences identified a modified sulfoglycolytic EMP gene cluster, conserved across a range of other Actinobacteria, that retained the core sulfoglycolysis genes encoding metabolic enzymes but featured the replacement of the gene encoding sulfolactaldehyde (SLA) reductase with SLA dehydrogenase, and the absence of sulfoquinovosidase and sulfoquinovose mutarotase genes. Excretion of sulfolactate by these Arthrobacter spp. is consistent with an aerobic saprophytic lifestyle. This work broadens our knowledge of the sulfo-EMP pathway to include soil bacteria.

Synthesis of the Alkylsulfonate Metabolites Cysteinolic Acid, 3-Amino-2-hydroxypropanesulfonate, and 2,3-Dihydroxypropanesulfonate

Chiral hydroxy- and aminohydroxysulfonic acids are widespread in the marine and terrestrial environment. Here we report simple methods for the synthesis of d- and l-cysteinolic acid (from (Boc-d-Cys-OH)₂ and (Boc-l-Cys-OH)₂, respectively), R- and S-3-amino-2-hydroxypropanesulfonate (from S- and R-epichlorohydrin, respectively), and R- and S-2,3-dihydroxypropanesulfonate (from S- and R-epichlorohydrin, respectively). d-Cysteinolate bile salts were generated by coupling with cholic and chenodeoxycholic acids. A series of single-crystal 3D X-ray structures confirmed the absolute configurations of the aminosulfonates. By comparison of optical rotation, we assign naturally occurring 3-amino-2-hydroxypropanesulfonate from Gateloupia livida as possessing the R-configuration. This simple synthetic approach will support future studies of the occurrence, chemotaxonomic distribution, and metabolism of these alkylsulfonates.

From the banal to the bizarre: unravelling immune recognition and response to microbial lipids

Microbes produce a rich array of lipidic species that through their location in the cell wall and ability to mingle with host lipids represent a privileged class of immune-active molecules. Lipid-sensing immunity recognizes microbial lipids from pathogens and commensals causing immune responses. Yet microbial lipids are often heterogeneous, in limited supply and in some cases their structures are incompletely defined. Total synthesis can assist in structural determination, overcome supply issues, and provide access to high-purity, homogeneous samples and analogues. This account highlights synthetic approaches to lipidic species from pathogenic and commensal bacteria and fungi that have supported immunological studies involving lipid sensing through the pattern recognition receptor Mincle and cell-mediated immunity through the CD1-T cell axis.

Characterization of Mycobacterium tuberculosis Mycolic Acids by Multiple-Stage Linear Ion-Trap Mass Spectrometry

Mycobacterium tuberculosis (Mtb) cells are known to synthesize very long chain (C60-90) structurally complex mycolic acids with various functional groups. In this study, we applied linear ion-trap (LIT) multiple-stage mass spectrometry (MSn), combined with high-resolution mass spectrometry to study the mechanisms underlying the fragmentation processes of mycolic acid standards desorbed as lithiated adduct ions by ESI. This is followed by structural characterization of a Mtb mycolic acid family (Bovine strain). Using the insight fragmentation processes gained from the study, we are able to achieve a near complete characterization of the whole mycolic acid family, revealing the identity of the α-alkyl chain, the location of the functional groups including methyl, methoxy, and keto groups along the meroaldehyde chain in each lipid species. This study showcased the power of LIT MSn toward structural determination of complex lipids in a mixture, which would be otherwise very difficult to define using other analytical techniques.

Sulfoglycolysis: catabolic pathways for metabolism of sulfoquinovose

Sulfoquinovose (SQ), a derivative of glucose with a C6-sulfonate, is produced by photosynthetic organisms and is the headgroup of the sulfolipid sulfoquinovosyl diacylglycerol. The degradation of SQ allows recycling of its elemental constituents and is important in the global sulfur and carbon biogeochemical cycles. Degradation of SQ by bacteria is achieved through a range of pathways that fall into two main groups. One group involves scission of the 6-carbon skeleton of SQ into two fragments with metabolic utilization of carbons 1-3 and excretion of carbons 4-6 as dihydroxypropanesulfonate or sulfolactate that is biomineralized to sulfite/sulfate by other members of the microbial community. The other involves the complete metabolism of SQ by desulfonylation involving cleavage of the C-S bond to release sulfite and glucose, the latter of which can enter glycolysis. The discovery of sulfoglycolytic pathways has revealed a wide range of novel enzymes and SQ binding proteins. Biochemical and structural characterization of the proteins and enzymes in these pathways have illuminated how the sulfonate group is recognized by Nature's catalysts, supporting bioinformatic annotation of sulfoglycolytic enzymes, and has identified functional and structural relationships with the pathways of glycolysis.

Solar simulated ultraviolet radiation inactivates HCoV-NL63 and SARS-CoV-2 coronaviruses at environmentally relevant doses

The germicidal properties of short wavelength ultraviolet C (UVC) light are well established and used to inactivate many viruses and other microbes. However, much less is known about germicidal effects of terrestrial solar UV light, confined exclusively to wavelengths in the UVA and UVB regions. Here, we have explored the sensitivity of the human coronaviruses HCoV-NL63 and SARS-CoV-2 to solar-simulated full spectrum ultraviolet light (sUV) delivered at environmentally relevant doses. First, HCoV-NL63 coronavirus inactivation by sUV-exposure was confirmed employing (i) viral plaque assays, (ii) RT-qPCR detection of viral genome replication, and (iii) infection-induced stress response gene expression array analysis. Next, a detailed dose-response relationship of SARS-CoV-2 coronavirus inactivation by sUV was elucidated, suggesting a half maximal suppression of viral infectivity at low sUV doses. Likewise, extended sUV exposure of SARS-CoV-2 blocked cellular infection as revealed by plaque assay and stress response gene expression array analysis. Moreover, comparative (HCoV-NL63 versus SARS-CoV-2) single gene expression analysis by RT-qPCR confirmed that sUV exposure blocks coronavirus-induced redox, inflammatory, and proteotoxic stress responses. Based on our findings, we estimate that solar ground level full spectrum UV light impairs coronavirus infectivity at environmentally relevant doses. Given the urgency and global scale of the unfolding SARS-CoV-2 pandemic, these prototype data suggest feasibility of solar UV-induced viral inactivation, an observation deserving further molecular exploration in more relevant exposure models.

Helicobacter pylori metabolites exacerbate gastritis through C-type lectin receptors

Helicobacter pylori causes gastritis, which has been attributed to the development of H. pylori-specific T cells during infection. However, the mechanism underlying innate immune detection leading to the priming of T cells is not fully understood, as H. pylori evades TLR detection. Here, we report that H. pylori metabolites modified from host cholesterol exacerbate gastritis through the interaction with C-type lectin receptors. Cholesteryl acyl α-glucoside (αCAG) and cholesteryl phosphatidyl α-glucoside (αCPG) were identified as noncanonical ligands for Mincle (Clec4e) and DCAR (Clec4b1). During chronic infection, H. pylori-specific T cell responses and gastritis were ameliorated in Mincle-deficient mice, although bacterial burdens remained unchanged. Furthermore, a mutant H. pylori strain lacking αCAG and αCPG exhibited an impaired ability to cause gastritis. Thus H. pylori-specific modification of host cholesterol plays a pathophysiological role that exacerbates gastric inflammation by triggering C-type lectin receptors.

Benzofuran sulfonates and small self-lipid antigens activate type II NKT cells via CD1d

Natural killer T (NKT) cells detect lipids presented by CD1d. Most studies focus on type I NKT cells that express semi-invariant αβ T cell receptors (TCR) and recognize α-galactosylceramides. However, CD1d also presents structurally distinct lipids to NKT cells expressing diverse TCRs (type II NKT cells), but our knowledge of the antigens for type II NKT cells is limited. An early study identified a nonlipidic NKT cell agonist, phenyl pentamethyldihydrobenzofuransulfonate (PPBF), which is notable for its similarity to common sulfa drugs, but its mechanism of NKT cell activation remained unknown. Here, we demonstrate that a range of pentamethylbenzofuransulfonates (PBFs), including PPBF, activate polyclonal type II NKT cells from human donors. Whereas these sulfa drug-like molecules might have acted pharmacologically on cells, here we demonstrate direct contact between TCRs and PBF-treated CD1d complexes. Further, PBF-treated CD1d tetramers identified type II NKT cell populations expressing αβTCRs and γδTCRs, including those with variable and joining region gene usage (TRAV12-1-TRAJ6) that was conserved across donors. By trapping a CD1d-type II NKT TCR complex for direct mass-spectrometric analysis, we detected molecules that allow the binding of CD1d to TCRs, finding that both selected PBF family members and short-chain sphingomyelin lipids are present in these complexes. Furthermore, the combination of PPBF and short-chain sphingomyelin enhances CD1d tetramer staining of PPBF-reactive T cell lines over either molecule alone. This study demonstrates that nonlipidic small molecules, which resemble sulfa drugs implicated in systemic hypersensitivity and drug allergy reactions, are targeted by a polyclonal population of type II NKT cells in a CD1d-restricted manner.

Solar simulated ultraviolet radiation inactivates HCoV-NL63 and SARS-CoV-2 coronaviruses at environmentally relevant doses

The germicidal properties of short wavelength ultraviolet C (UVC) light are well established and used to inactivate many viruses and other microbes. However, much less is known about germicidal effects of terrestrial solar UV light, confined exclusively to wavelengths in the UVA and UVB regions. Here, we have explored the sensitivity of the human coronaviruses HCoV-NL63 and SARS-CoV-2 to solar-simulated full spectrum ultraviolet light (sUV) delivered at environmentally relevant doses. First, HCoV-NL63 coronavirus inactivation by sUV-exposure was confirmed employing (i) viral plaque assays, (ii) RT-qPCR detection of viral genome replication, and (iii) infection-induced stress response gene expression array analysis. Next, a detailed dose-response relationship of SARS-CoV-2 coronavirus inactivation by sUV was elucidated, suggesting a half maximal suppression of viral infectivity at low sUV doses. Likewise, extended sUV exposure of SARS-CoV-2 blocked cellular infection as revealed by plaque assay and stress response gene expression array analysis. Moreover, comparative (HCoV-NL63 versus SARS-CoV-2) single gene expression analysis by RT-qPCR confirmed that sUV exposure blocks coronavirus-induced redox, inflammatory, and proteotoxic stress responses. Based on our findings, we estimate that solar ground level full spectrum UV light impairs coronavirus infectivity at environmentally relevant doses. Given the urgency and global scale of the unfolding SARS-CoV-2 pandemic, these prototype data suggest feasibility of solar UV-induced viral inactivation, an observation deserving further molecular exploration in more relevant exposure models.

Unimolecular, Bimolecular, and Intramolecular Hydrolysis Mechanisms of 4-Nitrophenyl β-d-Glucopyranoside

1,2-trans-Glycosides hydrolyze through different mechanisms at different pH values, but systematic studies are lacking. Here, we report the pH-rate constant profile for the hydrolysis of 4-nitrophenyl β-D-glucoside. An inverse kinetic isotope effect of k(H₃O⁺)/k(D₃O⁺) = 0.65 in the acidic region indicates that the mechanism requires the formation of the conjugate acid of the substrate for the reaction to proceed, with the heterolytic cleavage of the glycosidic C-O bond. Reactions in the pH-independent region exhibit general catalysis with a single proton in flight, a normal solvent isotope effect of k_H/k_D = 1.5, and when extrapolated to zero buffer concentration show a small solvent isotope effect of k(H₂O)/k(D₂O) = 1.1, consistent with water attack through a dissociative mechanism. In the basic region, solvolysis in ¹⁸O-labeled water and H₂O/MeOH mixtures allowed the detection of bimolecular hydrolysis and neighboring group participation, with a minor contribution of nucleophilic aromatic substitution. Under mildly basic conditions, a bimolecular concerted mechanism is implicated through an inverse solvent isotope effect of k(HO^-)/k(DO^-) = 0.5 and a strongly negative entropy of activation (ΔS^‡ = -13.6 cal mol^-1 K^-1). Finally, at high pH, an inverse solvent isotope effect of k(HO^-)/k(DO^-) = 0.5 indicates that the formation of 1,2-anhydrosugar is the rate-determining step.

Molecular Basis of Sulfosugar Selectivity in Sulfoglycolysis

The sulfosugar sulfoquinovose (SQ) is produced by essentially all photosynthetic organisms on Earth and is metabolized by bacteria through the process of sulfoglycolysis. The sulfoglycolytic Embden-Meyerhof-Parnas pathway metabolizes SQ to produce dihydroxyacetone phosphate and sulfolactaldehyde and is analogous to the classical Embden-Meyerhof-Parnas glycolysis pathway for the metabolism of glucose-6-phosphate, though the former only provides one C3 fragment to central metabolism, with excretion of the other C3 fragment as dihydroxypropanesulfonate. Here, we report a comprehensive structural and biochemical analysis of the three core steps of sulfoglycolysis catalyzed by SQ isomerase, sulfofructose (SF) kinase, and sulfofructose-1-phosphate (SFP) aldolase. Our data show that despite the superficial similarity of this pathway to glycolysis, the sulfoglycolytic enzymes are specific for SQ metabolites and are not catalytically active on related metabolites from glycolytic pathways. This observation is rationalized by three-dimensional structures of each enzyme, which reveal the presence of conserved sulfonate binding pockets. We show that SQ isomerase acts preferentially on the β-anomer of SQ and reversibly produces both SF and sulforhamnose (SR), a previously unknown sugar that acts as a derepressor for the transcriptional repressor CsqR that regulates SQ-utilization. We also demonstrate that SF kinase is a key regulatory enzyme for the pathway that experiences complex modulation by the metabolites SQ, SLA, AMP, ADP, ATP, F6P, FBP, PEP, DHAP, and citrate, and we show that SFP aldolase reversibly synthesizes SFP. This body of work provides fresh insights into the mechanism, specificity, and regulation of sulfoglycolysis and has important implications for understanding how this biochemistry interfaces with central metabolism in prokaryotes to process this major repository of biogeochemical sulfur.

Candida albicans steryl 6-O-acyl-α-D-mannosides agonize signalling through Mincle

The C-type lectin receptor Mincle binds Candida albicans and has been implicated in its pathobiology, but the molecular effectors responsible have not been identified. We report the synthesis of cholesteryl and ergosteryl 6-O-acyl-α-d-mannosides, produced by C. albicans mycelium, and demonstrate their ability to signal through human and mouse Mincle.

Cholesteryl 6-O-acyl-α-glucosides from diverse Helicobacter spp. signal through the C-type lectin receptor Mincle

Helicobacter spp. are Gram-negative bacteria that cause a spectrum of disease in the gut, biliary tree and liver. Many Helicobacter spp. produce a range of cholesteryl α-glucosides that have the potential to act as pathogen associated molecular patterns. We report a highly stereoselective α-glucosylation of cholesterol using 3,4,6-tri-O-acetyl-2-O-benzyl-d-glucopyranosyl N-phenyl-2,2,2-trifluoroacetimidate, which allowed the synthesis of cholesteryl α-glucoside (αCG) and representative Helicobacter spp. cholesteryl 6-O-acyl-α-glucosides (αCAGs; acyl = C12:0, 14:0, C16:0, C18:0, C18:1). All αCAGs, irrespective of the nature of their acyl chain composition, strongly agonised signalling through the C-type lectin receptor Mincle from human and mouse to similar degrees. By contrast, αCG only weakly signalled through human Mincle, and did not signal through mouse Mincle. These results provide a molecular basis for understanding of the immunobiology of non-pylori Helicobacter infections in humans and other animals.

An Epoxide Intermediate in Glycosidase Catalysis

Retaining glycoside hydrolases cleave their substrates through stereochemical retention at the anomeric position. Typically, this involves two-step mechanisms using either an enzymatic nucleophile via a covalent glycosyl enzyme intermediate or neighboring-group participation by a substrate-borne 2-acetamido neighboring group via an oxazoline intermediate; no enzymatic mechanism with participation of the sugar 2-hydroxyl has been reported. Here, we detail structural, computational, and kinetic evidence for neighboring-group participation by a mannose 2-hydroxyl in glycoside hydrolase family 99 endo-α-1,2-mannanases. We present a series of crystallographic snapshots of key species along the reaction coordinate: a Michaelis complex with a tetrasaccharide substrate; complexes with intermediate mimics, a sugar-shaped cyclitol β-1,2-aziridine and β-1,2-epoxide; and a product complex. The 1,2-epoxide intermediate mimic displayed hydrolytic and transfer reactivity analogous to that expected for the 1,2-anhydro sugar intermediate supporting its catalytic equivalence. Quantum mechanics/molecular mechanics modeling of the reaction coordinate predicted a reaction pathway through a 1,2-anhydro sugar via a transition state in an unusual flattened, envelope (E ₃) conformation. Kinetic isotope effects (k _cat/K _M) for anomeric-²H and anomeric-¹³C support an oxocarbenium ion-like transition state, and that for C2-¹⁸O (1.052 ± 0.006) directly implicates nucleophilic participation by the C2-hydroxyl. Collectively, these data substantiate this unprecedented and long-imagined enzymatic mechanism.

Design of potent Mincle signalling agonists based on an alkyl β-glucoside template

The innate immune receptor Mincle senses lipid-based molecules derived from pathogens, commensals and altered self. Based on emerging structure-activity relationships we design simple alkyl 6-O-acyl-β-d-glucosides that are effective agonists of Mincle and signal with potency on par with the prototypical ligand trehalose dimycolate.

Concise synthesis of sulfoquinovose and sulfoquinovosyl diacylglycerides, and development of a fluorogenic substrate for sulfoquinovosidases

The sulfolipid sulfoquinovosyl diacylglycerol (SQDG) and its headgroup, the sulfosugar sulfoquinovose (SQ), are estimated to harbour up to half of all organosulfur in the biosphere. SQ is liberated from SQDG and related glycosides by the action of sulfoquinovosidases (SQases). We report a 10-step synthesis of SQDG that we apply to the preparation of saturated and unsaturated lipoforms. We also report an expeditious synthesis of SQ and (¹³C₆)SQ, and X-ray crystal structures of sodium and potassium salts of SQ. Finally, we report the synthesis of a fluorogenic SQase substrate, methylumbelliferyl α-d-sulfoquinovoside, and examination of its cleavage kinetics by two recombinant SQases. These compounds will assist in dissecting the role of sulfoglycolysis in the biogeochemical sulfur cycle and understanding the molecular basis of sulfoglycolysis.

α-Glucuronosyl and α-glucosyl diacylglycerides, natural killer T cell-activating lipids from bacteria and fungi

Natural killer T cells express T cell receptors (TCRs) that recognize glycolipid antigens in association with the antigen-presenting molecule CD1d. Here, we report the concise chemical synthesis of a range of saturated and unsaturated α-glucosyl and α-glucuronosyl diacylglycerides of bacterial and fungal origins from allyl α-glucoside with Jacobsen kinetic resolution as a key step. These glycolipids are recognized by a classical type I NKT TCR that uses an invariant Vα14-Jα18 TCR α-chain, but also by an atypical NKT TCR that uses a different TCR α-chain (Vα10-Jα50). In both cases, recognition is sensitive to the lipid fine structure, and includes recognition of glycosyl diacylglycerides bearing branched (R- and S-tuberculostearic acid) and unsaturated (oleic and vaccenic) acids. The TCR footprints on CD1d loaded with a mycobacterial α-glucuronosyl diacylglyceride were assessed using mutant CD1d molecules and, while similar to that for α-GalCer recognition by a type I NKT TCR, were more sensitive to mutations when α-glucuronosyl diacylglyceride was the antigen. In summary, we provide an efficient approach for synthesis of a broad class of bacterial and fungal α-glycosyl diacylglyceride antigens and demonstrate that they can be recognised by TCRs derived from type I and atypical NKT cells.

Microbial α-glycosyl diacylglycerides when presented by the antigen presenting molecule CD1d are recognized by both classical type I and atypical Natural Killer T cell receptors.

Mannosidase mechanism: at the intersection of conformation and catalysis

Mannosidases are a diverse group of enzymes that are important in the biological processing of mannose-containing polysaccharides and complex glycoconjugates. They are found in 12 of the >160 sequence-based glycosidase families. We discuss evidence that nature has evolved a small set of common mechanisms that unite almost all of these mannosidase families. Broadly, mannosidases (and the closely related rhamnosidases) perform catalysis through just two conformations of the oxocarbenium ion-like transition state: a B_2,5 (or enantiomeric ^2,5B) boat and a ³H₄ half-chair. This extends to a new family (GT108) of GDPMan-dependent β-1,2-mannosyltransferases/phosphorylases that perform mannosyl transfer through a boat conformation as well as some mannosidases that are metalloenzymes and require divalent cations for catalysis. Yet, among this commonality lies diversity. New evidence shows that one unique family (GH99) of mannosidases use an unusual mechanism involving anchimeric assistance via a 1,2-anhydro sugar (epoxide) intermediate.

Distinct CD1d docking strategies exhibited by diverse Type II NKT cell receptors

Type I and type II natural killer T (NKT) cells are restricted to the lipid antigen-presenting molecule CD1d. While we have an understanding of the antigen reactivity and function of type I NKT cells, our knowledge of type II NKT cells in health and disease remains unclear. Here we describe a population of type II NKT cells that recognise and respond to the microbial antigen, α-glucuronosyl-diacylglycerol (α-GlcADAG) presented by CD1d, but not the prototypical type I NKT cell agonist, α-galactosylceramide. Surprisingly, the crystal structure of a type II NKT TCR-CD1d-α-GlcADAG complex reveals a CD1d F’-pocket-docking mode that contrasts sharply with the previously determined A’-roof positioning of a sulfatide-reactive type II NKT TCR. Our data also suggest that diverse type II NKT TCRs directed against distinct microbial or mammalian lipid antigens adopt multiple recognition strategies on CD1d, thereby maximising the potential for type II NKT cells to detect different lipid antigens.

Natural killer T (NKT) cells include type I that express semi-invariant T cell receptor (TCR), and type II that cover a broader repertoire. Here the authors describe the crystal structure of a type II NKT TCR complexed with CD1d/antigen to propose that type II NKT TCRs may adapt multiple CD1d docking modes to maximise antigen recognition efficacy.

Glutathione contributes to efficient post-Golgi trafficking of incoming HPV16 genome

Human papillomavirus (HPV) is the most common sexually transmitted pathogen in the United States, causing 99% of cervical cancers and 5% of all human cancers worldwide. HPV infection requires transport of the viral genome (vDNA) into the nucleus of basal keratinocytes. During this process, minor capsid protein L2 facilitates subcellular retrograde trafficking of the vDNA from endosomes to the Golgi, and accumulation at host chromosomes during mitosis for nuclear retention and localization during interphase. Here we investigated the relationship between cellular glutathione (GSH) and HPV16 infection. siRNA knockdown of GSH biosynthetic enzymes results in a partial decrease of HPV16 infection. Likewise, infection of HPV16 in GSH depleted keratinocytes is inefficient, an effect that was not seen with adenoviral vectors. Analysis of trafficking revealed no defects in cellular binding, entry, furin cleavage of L2, or retrograde trafficking of HPV16, but GSH depletion hindered post-Golgi trafficking and translocation, decreasing nuclear accumulation of vDNA. Although precise mechanisms have yet to be defined, this work suggests that GSH is required for a specific post-Golgi trafficking step in HPV16 infection.

Synthetic β-1,2-Mannosyloxymannitol Glycolipid from the Fungus Malassezia pachydermatis Signals through Human Mincle

Mincle is a C-type lectin receptor of the innate immune system with the ability to sense pathogens and commensals through lipidic metabolites. While a growing number of bacterial glycolipids have been discovered that can signal through human Mincle, no fungal metabolites are known that can signal through the human form of this receptor. We report the total synthesis of a complex β-1,2-mannosyloxymannitol glycolipid from Malassezia pachydermatis 44-2, which was reported to signal through the murine Mincle receptor. Assembly of 44-2 was achieved through a highly convergent route that exploits symmetry elements inherent within this molecule and delineation of conditions that maintain the delicate l-mannitol triester-triol array. We show that 44-2 is a potent agonist of human Mincle signaling and constitutes the first fungal metabolite identified that can signal through the human Mincle receptor, providing new insights into antifungal immunity.

Discovery of N-Aryloxypropylbenzylamines as Voltage-Gated Sodium Channel NaV 1.2-Subtype-Selective Inhibitors

We previously reported that a lipophilic N-(4'-hydroxy-3',5'-di-tert-butylbenzyl) derivative (1) of the voltage-gated sodium channel blocker mexiletine, was a more potent sodium channel blocker in vitro and in vivo. We demonstrate that replacing the chiral methylethylene linker between the amine and di-tert-butylphenol with an achiral 1,3-propylene linker (to give (2)) maintains potency in vitro. We synthesized 25 analogues bearing the 1,3-propylene linker and found that minor structural changes resulted in pronounced changes in state dependence of blocking human Na_V 1.2 and 1.6 channels by high-throughput patch-clamp analysis. Compared to mexiletine, compounds 1 and 2 are highly selective Na_V 1.2 inhibitors and >500 times less potent in inhibiting Na_V 1.6 channels. On the other hand, a derivative (compound 4) bearing 2,6-dimethoxy groups in place of the 2,6-dimethyl groups found in mexiletine was found to be the most potent inhibitor, but is nonselective against both channels in the tonic, frequency-dependent and inactivated states. In a kindled mouse model of refractory epilepsy, compound 2 inhibited seizures induced by 6 Hz 44 mA electrical stimulation with an IC₅₀ value of 49.9±1.6 mg kg^-1 . As established sodium channel blockers do not suppress seizures in this mouse model, this indicates that 2 could be a promising candidate for treating pharmaco-resistant epilepsy.

Diazepam is not a direct allosteric modulator of α1-adrenoceptors, but modulates receptor signaling by inhibiting phosphodiesterase-4

α1A- and α1B-adrenoceptors (ARs) are G protein-coupled receptors (GPCRs) that are activated by adrenaline and noradrenaline to modulate smooth muscle contraction in the periphery, and neuronal outputs in the central nervous system (CNS). α1A- and α1B-AR are clinically targeted with antagonists for hypertension and benign prostatic hyperplasia and are emerging CNS targets for treating neurodegenerative diseases. The benzodiazepines midazolam, diazepam, and lorazepam are proposed to be positive allosteric modulators (PAMs) of α1-ARs. Here, using thermostabilized, purified, α1A- and α1B-ARs, we sought to identify the benzodiazepine binding site and modulatory mechanism to inform the design of selective PAMs. However, using a combination of biophysical approaches no evidence was found for direct binding of several benzodiazepines to purified, stabilized α1A- and α1B-ARs. Similarly, in cell-based assays expressing unmodified α1A- and α1B-ARs, benzodiazepine treatment had no effect on fluorescent ligand binding, agonist-stimulated Ca2+ release, or G protein activation. In contrast, several benzodiazepines positively modulated phenylephrine stimulation of a cAMP response element pathway by α1A- and α1B-ARs; however, this was shown to be caused by off-target inhibition of phosphodiesterases, known targets of diazepam. This study highlights how purified, stabilized GPCRs are useful for validating allosteric ligand binding and that care needs to be taken before assigning new targets to benzodiazepines.

Distortion of mannoimidazole supports a B2,5 boat transition state for the family GH125 α-1,6-mannosidase from Clostridium perfringens

Enzyme transition-state mimics can act as powerful inhibitors and allow structural studies that report on the conformation of the transition-state.

Structural and Biochemical Insights into the Function and Evolution of Sulfoquinovosidases

An estimated 10 billion tonnes of sulfoquinovose (SQ) are produced and degraded each year. Prokaryotic sulfoglycolytic pathways catabolize sulfoquinovose (SQ) liberated from plant sulfolipid, or its delipidated form α-d-sulfoquinovosyl glycerol (SQGro), through the action of a sulfoquinovosidase (SQase), but little is known about the capacity of SQ glycosides to support growth. Structural studies of the first reported SQase (Escherichia coli YihQ) have identified three conserved residues that are essential for substrate recognition, but crossover mutations exploring active-site residues of predicted SQases from other organisms have yielded inactive mutants casting doubt on bioinformatic functional assignment. Here, we show that SQGro can support the growth of E. coli on par with d-glucose, and that the E. coli SQase prefers the naturally occurring diastereomer of SQGro. A predicted, but divergent, SQase from Agrobacterium tumefaciens proved to have highly specific activity toward SQ glycosides, and structural, mutagenic, and bioinformatic analyses revealed the molecular coevolution of catalytically important amino acid pairs directly involved in substrate recognition, as well as structurally important pairs distal to the active site. Understanding the defining features of SQases empowers bioinformatic approaches for mapping sulfur metabolism in diverse microbial communities and sheds light on this poorly understood arm of the biosulfur cycle.

Abstract 426: Stress-induced Kinase Targets of Cardioprotective 3’,4’-dihydroxyflavonol in Injured Myocardium

3’,4’-dihydroxyflavonol (DiOHF) is a synthetic flavonol in a class of phytochemicals known as flavonoids can have beneficial biological properties. Previous studies revealed that intravenous administration of DiOHF immediately preceding myocardial reperfusion potently reduced infarct size in anaesthetised sheep that was comparable to ischemic preconditioning and the protective effects of DiOHF were recapitulated ex vivo during ischemia/reperfusion (I/R) of Langendorff-perfused rat hearts and in vitro on isolated cardiac myocytes. These studies highlight the therapeutic potential of DiOHF, with derivatives recently entering Phase II trials for the reduction of ventricular injury and contractile dysfunction following myocardial infarction (NCT02557217). In our current study, we confirmed potent cytoprotective effects of DiOHF in preventing apoptotic and necrotic death of primary rat cardiomyocytes. In addition, we revealed potent anti-hypertrophic effects in cardiomyocytes stimulated with alpha and beta-adrenergic agonists. In comparison with structurally similar compounds, fisetin, quercetin and dihydroxyflavone, DiOHF exhibited enhanced anti-hypertrophic and protective properties. The molecular targets of DiOHF that underpin it’s beneficial effects are of immense interest as they aid clinical development of derivative compounds, rational design of new compounds with biological activity and provide novel insights into the regulatory mechanisms that define the protected myocardium. In exploring the DiOHF mechanisms of action, we had previously reported DiOHF inhibited Ca2+/calmodulin dependent protein kinase II (CaMKII) activity in in vitro kinase assays and in cultured myoblasts. Here, we used resin-immobilized DiOHF for affinity purification from heart tissue lysates and confirmed direct drug-interaction with CaMKII/p-CaMKII from injured rat myocardium (I/R). In addition, we revealed DiOHF interaction and direct inhibition of apoptosis-signal regulated kinase (ASK1) from I/R rat hearts. Our ongoing studies will define whether flavonol inhibition of CaMKII and ASK1 defines protective benefits of DiOHF in the injured myocardium.

The galanin receptor-3 antagonist, SNAP 37889, inhibits cue-induced reinstatement of alcohol-seeking and increases c-Fos expression in the nucleus accumbens shell of alcohol-preferring rats

INTRODUCTION

This study aimed to investigate the effects of the galanin-3 receptor antagonist, SNAP 37889, on c-Fos protein expression after cue-induced reinstatement of alcohol-seeking in the brains of alcohol-preferring rats.

METHODS

Eighteen alcohol-preferring rats were trained to self-administer 10% v/v ethanol in the presence of response-contingent cues, which was followed by extinction. Rats were then treated with SNAP 37889 (30 mg/kg, i.p.) or vehicle, before being tested for cue-induced reinstatement. Administration of SNAP 37889 reduced cue-induced reinstatement of ethanol-seeking behaviour. To examine the effect of SNAP 37889 and cue-induced reinstatement on neuronal activation, c-Fos expression was measured in subregions of the medial prefrontal cortex and nucleus accumbens.

RESULTS

SNAP 37889 administration increased c-Fos immunoreactivity in the nucleus accumbens shell, but was without effect in the nucleus accumbens core and the medial prefrontal cortex. Dual-label Fos/tyrosine hydroxylase immunohistochemistry was used to examine the effects of SNAP 37889 on dopamine neurons in the ventral tegmental area; however, no differences between SNAP 37889 and vehicle-treated rats were found.

CONCLUSIONS

These data support previous findings of galanin-3 receptor involvement in cue-induced reinstatement of alcohol-seeking behaviour, and provide novel evidence that the ability of galanin-3 receptor antagonism to attenuate cue-induced reinstatement relates to activation of the nucleus accumbens shell.

Gram scale preparation of clozapine N-oxide (CNO), a synthetic small molecule actuator for muscarinic acetylcholine DREADDs

Chemogenetics uses engineered proteins that are controlled by small molecule actuators, allowing in vivo functional studies of proteins with temporal and dose control, and include Designer Receptors Exclusively Activated by Designer Drugs (DREADDs). One major class of DREADDs are mutated muscarinic receptors that are unresponsive to acetylcholine, and are activated by administration of clozapine N-oxide (CNO). However, CNO is available in only small amounts and large scale studies involving animals and multiple cohorts are prohibitively expensive for many investigators. The precursor, clozapine, is also expensive when purchased from specialist suppliers. Here we report:

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A simple extraction method of clozapine from commercial tablets;

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A simple preparation of CNO from clozapine, and for the first time its single-crystal X-ray structure; and

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That the CNO prepared by this method specifically activates the DREADD receptor hM3Dq in vivo.

This method provides large quantities of CNO suitable for large-scale DREADD applications that is identical to commercial material.