Chemotactic Interactions Drive Migration of Membraneless Active Droplets.

In nature, chemotactic interactions are ubiquitous and play a critical role in driving the collective behavior of living organisms. Reproducing these interactions in vitro is still a paramount challenge due to the complexity of mimicking and controlling cellular features, such as tangled metabolic networks, cytosolic macromolecular crowding, and cellular migration, on a microorganism size scale. Here, we generate enzymatically active cell-sized droplets able to move freely, and by following a chemical gradient, able to interact with the surrounding droplets in a collective manner. The enzyme within the droplets generates a pH gradient that extends outside the edge of the droplets. We discovered that the external pH gradient triggers droplet migration and controls its directionality, which is selectively toward the neighboring droplets. Hence, by changing the enzyme activity inside the droplet, we tuned the droplet migration speed. Furthermore, we showed that these cellular-like features can facilitate the reconstitution of a simple and linear protometabolic pathway and increase the final reaction product generation. Our work suggests that simple and stable membraneless droplets can reproduce complex biological phenomena, opening new perspectives as bioinspired materials and synthetic biology tools.

Biochemical and cellular effects of a novel missense mutation of the AGXT gene associated with Primary Hyperoxaluria Type 1.

Primary Hyperoxaluria Type 1 (PH1) is a rare autosomal disease caused by mutations in AGXT that lead to the deficiency of alanine:glyoxylate aminotransferase (AGT). AGT is a liver pyridoxal 5'-phosphate (PLP)-dependent enzyme that detoxifies glyoxylate inside peroxisomes. The lack of AGT activity results in a build-up of glyoxylate that is oxidized to oxalate, then culminating in hyperoxaluria often leading to kidney failure. Most pathogenic mutations reduce AGT specific activity because of catalytic defects, improper folding, mistargeting to mitochondria, reduced intracellular stability, dimerization, and/or aggregation. Administration of pyridoxine (PN), a precursor of PLP, is a therapeutic option available for PH1 patients carrying responsive genotypes through the ability of the coenzyme to behave as a chaperone. Here, we report the clinical and biochemical characterization of the novel mutation c.1093G > T (p.Gly365Cys) identified in a Japanese patient. In silico studies predict that the p.Gly365Cys mutation causes a steric clash resulting in a local rearrangement of the region surrounding the active site, thus possibly affecting PLP binding and catalysis. Indeed, the purified p.Gly365Cys mutant displays proper folding but shows an extensive decrease of catalytic efficiency due to an altered PLP-binding. When expressed in AGXT1-KO HepG2 cells the variant shows reduced specific activity and protein levels in comparison with wild type AGT that cannot be rescued by PN treatment. Overall, our data indicate that the mutation of Gly365 induces a conformational change at the AGT active site translating into a functional and structural defect and allow to predict that the patients will not be responsive to vitamin B6, thus supporting the usefulness of preclinical studies to guide therapeutic decisions in the era of precision medicine.

Crystal structure of Aspergillus fumigatus AroH, an aromatic amino acid aminotransferase.

Aspergillus fumigatus is a saprophytic ubiquitous fungus whose spores can trigger reactions such as allergic bronchopulmonary aspergillosis or the fatal invasive pulmonary aspergillosis. To survive in the lungs, the fungus must adapt to a hypoxic and nutritionally restrictive environment, exploiting the limited availability of aromatic amino acids (AAAs) in the best possible way, as mammals do not synthesize them. A key enzyme for AAAs catabolism in A. fumigatus is AroH, a pyridoxal 5'-phosphate-dependent aromatic aminotransferase. AroH was recently shown to display a broad substrate specificity, accepting L-kynurenine and α-aminoadipate as amino donors besides AAAs. Given its pivotal role in the adaptability of the fungus to nutrient conditions, AroH represents a potential target for the development of innovative therapies against A. fumigatus-related diseases. We have solved the crystal structure of Af-AroH at 2.4 Å resolution and gained new insight into the dynamics of the enzyme's active site, which appears to be crucial for the design of inhibitors. The conformational plasticity of the active site pocket is probably linked to the wide substrate specificity of AroH.

The ILE56 mutation on different genetic backgrounds of alanine:glyoxylate aminotransferase: Clinical features and biochemical characterization.

Primary Hyperoxaluria type I (PH1) is a rare disease caused by mutations in the AGXT gene encoding alanine:glyoxylate aminotransferase (AGT), a liver enzyme involved in the detoxification of glyoxylate, the failure of which results in accumulation of oxalate and kidney stones formation. The role of protein misfolding in the AGT deficit caused by most PH1-causing mutations is increasingly being recognized. In addition, the genetic background in which a mutation occurs is emerging as a critical risk factor for disease onset and/or severity. Based on these premises, in this study we have analyzed the clinical, biochemical and cellular effects of the p.Ile56Asn mutation, recently described in a PH1 patient, as a function of the residue at position 11, a hot-spot for both polymorphic (p.Pro11Leu) and pathogenic (p.Pro11Arg) mutations. We have found that the p.Ile56Asn mutation induces a structural defect mostly related to the apo-form of AGT. The effects are more pronounced when the substitution of Ile56 is combined with the p.Pro11Leu and, at higher degree, the p.Pro11Arg mutation. As compared with the non-pathogenic forms, AGT variants display reduced expression and activity in mammalian cells. Vitamin B6, a currently approved treatment for PH1, can overcome the effects of the p.Ile56Asn mutation only when it is associated with Pro at position 11. Our results provide a first proof that the genetic background influences the effects of PH1-causing mutations and the responsiveness to treatment and suggest that molecular and cellular studies can integrate clinical data to identify the best therapeutic strategy for PH1 patients.

New variants of AADC deficiency expand the knowledge of enzymatic phenotypes.

AADC deficiency is a rare genetic disease caused by mutations in the gene of aromatic amino acid decarboxylase, the pyridoxal 5'-phosphate dependent enzyme responsible for the synthesis of dopamine and serotonin. Here, following a biochemical approach together with an in silico bioinformatic analysis, we present a structural and functional characterization of 13 new variants of AADC. The amino acid substitutions are spread over the entire protein from the N-terminal (V60A), to its loop1 (H70Y and F77L), to the large domain (G96R) and its various motifs, i.e. loop2 (A110E), or a core ß-barrel either on the surface (P210L, F251S and E283A) or in a more hydrophobic milieu (L222P, F237S and W267R) or loop3 (L353P), and to the C-terminal domain (R453C). Results show that the ß-barrel variants exhibit a low solubility and those belonging to the surface tend to aggregate in their apo form, leading to the identification of a new enzymatic phenotype for AADC deficiency. Moreover, five variants of residues belonging to the large interface of AADC (V60A, G96R, A110E, L353P and R453C) are characterized by a decreased catalytic efficiency. The remaining ones (H70Y and F77L) present features typical of apo-to-holo impaired transition. Thus, defects in catalysis or in the acquirement of the correct holo structure are due not only to specific local domain effects but also to long-range effects at either the protein surface or the subunit interface. Altogether, the new characterized enzymatic phenotypes represent a further step in the elucidation of the molecular basis for the disease.

Evolution of chalcone isomerase from a noncatalytic ancestor.

The emergence of catalysis in a noncatalytic protein scaffold is a rare, unexplored event. Chalcone isomerase (CHI), a key enzyme in plant flavonoid biosynthesis, is presumed to have evolved from a nonenzymatic ancestor related to the widely distributed fatty-acid binding proteins (FAPs) and a plant protein family with no isomerase activity (CHILs). Ancestral inference supported the evolution of CHI from a protein lacking isomerase activity. Further, we identified four alternative founder mutations, i.e., mutations that individually instated activity, including a mutation that is not phylogenetically traceable. Despite strong epistasis in other cases of protein evolution, CHI's laboratory reconstructed mutational trajectory shows weak epistasis. Thus, enantioselective CHI activity could readily emerge despite a catalytically inactive starting point. Accordingly, X-ray crystallography, NMR, and molecular dynamics simulations reveal reshaping of the active site toward a productive substrate-binding mode and repositioning of the catalytic arginine that was inherited from the ancestral fatty-acid binding proteins.

Publisher Correction: Evolution of chalcone isomerase from a noncatalytic ancestor.

In the version of this article originally published, the number for the equal contributions footnote was missing for Miriam Kaltenbach and Jason R. Burke in the author list. The error has been corrected in the PDF and print versions of this article.

Cycloserine enantiomers are reversible inhibitors of human alanine:glyoxylate aminotransferase: implications for Primary Hyperoxaluria type 1.

Peroxisomal alanine:glyoxylate aminotransferase (AGT) is responsible for glyoxylate detoxification in human liver and utilizes pyridoxal 5'-phosphate (PLP) as coenzyme. The deficit of AGT leads to Primary Hyperoxaluria Type I (PH1), a rare disease characterized by calcium oxalate stones deposition in the urinary tract as a consequence of glyoxylate accumulation. Most missense mutations cause AGT misfolding, as in the case of the G41R, which induces aggregation and proteolytic degradation. We have investigated the interaction of wild-type AGT and the pathogenic G41R variant with d-cycloserine (DCS, commercialized as Seromycin), a natural product used as a second-line treatment of multidrug-resistant tuberculosis, and its synthetic enantiomer l-cycloserine (LCS). In contrast with evidences previously reported on other PLP-enzymes, both ligands are AGT reversible inhibitors showing inhibition constants in the micromolar range. While LCS undergoes half-transamination generating a ketimine intermediate and behaves as a classical competitive inhibitor, DCS displays a time-dependent binding mainly generating an oxime intermediate. Using a mammalian cellular model, we found that DCS, but not LCS, is able to promote the correct folding of the G41R variant, as revealed by its increased specific activity and expression as a soluble protein. This effect also translates into an increased glyoxylate detoxification ability of cells expressing the variant upon treatment with DCS. Overall, our findings establish that DCS could play a role as pharmacological chaperone, thus suggesting a new line of intervention against PH1 based on a drug repositioning approach. To a widest extent, this strategy could be applied to other disease-causing mutations leading to AGT misfolding.

Pyridoxal 5'-Phosphate-Dependent Enzymes at the Crossroads of Host-Microbe Tryptophan Metabolism.

The chemical processes taking place in humans intersects the myriad of metabolic pathways occurring in commensal microorganisms that colonize the body to generate a complex biochemical network that regulates multiple aspects of human life. The role of tryptophan (Trp) metabolism at the intersection between the host and microbes is increasingly being recognized, and multiple pathways of Trp utilization in either direction have been identified with the production of a wide range of bioactive products. It comes that a dysregulation of Trp metabolism in either the host or the microbes may unbalance the production of metabolites with potential pathological consequences. The ability to redirect the Trp flux to restore a homeostatic production of Trp metabolites may represent a valid therapeutic strategy for a variety of pathological conditions, but identifying metabolic checkpoints that could be exploited to manipulate the Trp metabolic network is still an unmet need. In this review, we put forward the hypothesis that pyridoxal 5'-phosphate (PLP)-dependent enzymes, which regulate multiple pathways of Trp metabolism in both the host and in microbes, might represent critical nodes and that modulating the levels of vitamin B6, from which PLP is derived, might represent a metabolic checkpoint to re-orienteer Trp flux for therapeutic purposes.

Biochemical properties and oxalate-degrading activity of oxalate decarboxylase from bacillus subtilis at neutral pH.

Oxalate decarboxylase (OxDC) from Bacillus subtilis is a Mn-dependent hexameric enzyme that converts oxalate to carbon dioxide and formate. OxDC has greatly attracted the interest of the scientific community, mainly due to its biotechnological and medical applications in particular for the treatment of hyperoxaluria, a group of pathologic conditions caused by oxalate accumulation. The enzyme has an acidic optimum pH, but most of its applications involve processes occurring at neutral pH. Nevertheless, a detailed biochemical characterization of the enzyme at neutral pH is lacking. Here, we compared the structural-functional properties at acidic and neutral pH of wild-type OxDC and of a mutant form, called OxDC-DSSN, bearing four amino acid substitutions in the lid (Ser161-to-Asp, Glu162-to-Ser, Asn163-toSer, and Ser164-to-Asn) that improve the oxalate oxidase activity and almost abolish the decarboxylase activity. We found that both enzymatic forms do not undergo major structural changes as a function of pH, although OxDC-DSSN displays an increased tendency to aggregation, which is counteracted by the presence of an active-site ligand. Notably, OxDC and OxDC-DSSN at pH 7.2 retain 7 and 15% activity, respectively, which is sufficient to degrade oxalate in a cellular model of primary hyperoxaluria type I, a rare inherited disease caused by excessive endogenous oxalate production. The significance of the data in the light of the possible use of OxDC as biological drug is discussed. © 2019 IUBMB Life, 1-11, 2019.

Correlation between the molecular effects of mutations at the dimer interface of alanine-glyoxylate aminotransferase leading to primary hyperoxaluria type I and the cellular response to vitamin B6.

Primary hyperoxaluria type I (PH1) is a rare disease caused by the deficit of liver alanine-glyoxylate aminotransferase (AGT). AGT prevents oxalate formation by converting peroxisomal glyoxylate to glycine. When the enzyme is deficient, progressive calcium oxalate stones deposit first in the urinary tract and then at the systemic level. Pyridoxal 5'-phosphate (PLP), the AGT coenzyme, exerts a chaperone role by promoting dimerization, as demonstrated by studies at protein and cellular level. Thus, variants showing a destabilized dimeric structure should, in principle, be responsive to vitamin B6, a precursor of PLP. However, models to predict the extent of responsiveness of each variant are missing. We examined the effects of pathogenic interfacial mutations by combining bioinformatic predictions with molecular and cellular studies on selected variants (R36H, G42E, I56N, G63R, and G216R), in both their holo- (i.e., with bound PLP) and apo- (i.e., without bound PLP) form. We found that all variants displayed structural alterations mainly related to the apoform and consisting of an altered tertiary and quaternary structure. G216R also shows a strongly reduced catalytic efficiency. Moreover, all but G216R respond to vitamin B6, as shown by their increased specific activity and expression level in a cellular disease model. A global analysis of data unraveled a possible inverse correlation between the degree of destabilization/misfolding induced by a mutation and the extent of B6 responsiveness. These results provide a first explanation of factors influencing B6 response in PH1, a model possibly valuable for other rare diseases caused by protein deficits.

Folding Defects Leading to Primary Hyperoxaluria.

Protein misfolding is becoming one of the main mechanisms underlying inherited enzymatic deficits. This review is focused on primary hyperoxalurias, a group of disorders of glyoxylate detoxification associated with massive calcium oxalate deposition mainly in the kidneys. The most common and severe form, primary hyperoxaluria Type I, is due to the deficit of liver peroxisomal alanine/glyoxylate aminotransferase (AGT). Various studies performed in the last decade clearly evidence that many pathogenic missense mutations prevent the AGT correct folding, leading to various downstream effects including aggregation, increased degradation or mistargeting to mitochondria. Primary hyperoxaluria Type II and primary hyperoxaluria Type III are due to the deficit of glyoxylate reductase/hydroxypyruvate reductase (GRHPR) and 4-hydroxy-2-oxoglutarate aldolase (HOGA1), respectively. Although the molecular features of pathogenic variants of GRHPR and HOGA1 have not been investigated in detail, the data available suggest that some of them display folding defects. Thus, primary hyperoxalurias can be ranked among protein misfolding disorders, because in most cases the enzymatic deficit is due to the inability of each enzyme to reach its native and functional conformation. It follows that molecules able to improve the folding yield of the enzymes involved in each disease form could represent new therapeutic strategies.

The novel R347g pathogenic mutation of aromatic amino acid decarboxylase provides additional molecular insights into enzyme catalysis and deficiency.

We report here a clinical case of a patient with a novel mutation (Arg347→Gly) in the gene encoding aromatic amino acid decarboxylase (AADC) that is associated with AADC deficiency. The variant R347G in the purified recombinant form exhibits, similarly to the pathogenic mutation R347Q previously studied, a 475-fold drop of kcat compared to the wild-type enzyme. In attempting to unravel the reason(s) for this catalytic defect, we have carried out bioinformatics analyses of the crystal structure of AADC-carbidopa complex with the modelled catalytic loop (residues 328-339). Arg347 appears to interact with Phe103, as well as with both Leu333 and Asp345. We have then prepared and characterized the artificial F103L, R347K and D345A mutants. F103L, D345A and R347K exhibit about 13-, 97-, and 345-fold kcat decrease compared to the wild-type AADC, respectively. However, unlike F103L, the R347G, R347K and R347Q mutants as well as the D345A variant appear to be more defective in catalysis than in protein folding. Moreover, the latter mutants, unlike the wild-type protein and the F103L variant, share a peculiar binding mode of dopa methyl ester consisting of formation of a quinonoid intermediate. This finding strongly suggests that their catalytic defects are mainly due to a misplacement of the substrate at the active site. Taken together, our results highlight the importance of the Arg347-Leu333-Asp345 hydrogen-bonds network in the catalysis of AADC and reveal the molecular basis for the pathogenicity of the variants R347. Following the above results, a therapeutic treatment for patients bearing the mutation R347G is proposed.

Misfolding caused by the pathogenic mutation G47R on the minor allele of alanine:glyoxylate aminotransferase and chaperoning activity of pyridoxine.

Liver peroxisomal alanine:glyoxylate aminotransferase (AGT), a pyridoxal 5'-phosphate (PLP) enzyme, exists as two polymorphic forms, the major (AGT-Ma) and the minor (AGT-Mi) haplotype. Deficit of AGT causes Primary Hyperoxaluria Type 1 (PH1), an autosomal recessive rare disease. Although ~one-third of the 79 disease-causing missense mutations segregates on AGT-Mi, only few of them are well characterized. Here for the first time the molecular and cellular defects of G47R-Mi are reported. When expressed in Escherichia coli, the recombinant purified G47R-Mi variant exhibits only a 2.5-fold reduction of its kcat, and its apo form displays a remarkably decreased PLP binding affinity, increased dimer-monomer equilibrium dissociation constant value, susceptibility to thermal denaturation and to N-terminal region proteolytic cleavage, and aggregation propensity. When stably expressed in a mammalian cell line, we found ~95% of the intact form of the variant in the insoluble fraction, and proteolyzed (within the N-terminal region) and aggregated forms both in the soluble and insoluble fractions. Moreover, the intact and nicked forms have a peroxisomal and a mitochondrial localization, respectively. Unlike what already seen for G41R-Mi, exposure of G47R-Mi expressing cells to pyridoxine (PN) remarkably increases the expression level and the specific activity in a dose-dependent manner, reroutes all the protein to peroxisomes, and rescues its functionality. Although the mechanism of the different effect of PN on the variants G47R-Mi and G41R-Mi remains elusive, the chaperoning activity of PN may be of value in the therapy of patients bearing the G47R mutation.

A comprehensive picture of the mutations associated with aromatic amino acid decarboxylase deficiency: from molecular mechanisms to therapy implications.

Dopa decarboxylase (DDC), or aromatic amino acid decarboxylase (AADC), is a pyridoxal 5'-phosphate enzyme responsible for the production of the neurotransmitters dopamine and serotonin. Deficit of this enzyme causes AADC deficiency, an inherited neurometabolic disorder. To date, 18 missense homozygous mutations have been identified through genetic screening in ∼80 patients. However, little is known about the mechanism(s) by which mutations cause disease. Here we investigated the impact of these pathogenic mutations and of an artificial one on the conformation and the activity of wild-type DDC by a combined approach of bioinformatic, spectroscopic and kinetic analyses. All mutations reduce the kcat value, and, except the mutation R347Q, alter the tertiary structure, as revealed by an increased hydrophobic surface and a decreased near-UV circular dichroism signal. The integrated analysis of the structural and functional consequences of each mutation strongly suggests that the reason underlying the pathogenicity of the majority of disease-causing mutations is the incorrect apo-holo conversion. In fact, the most remarkable effects are seen upon mutation of residues His70, His72, Tyr79, Phe80, Pro81, Arg462 and Arg447 mapping to or directly interacting with loop1, a structural key element involved in the apo-holo switch. Instead, different mechanisms are responsible for the pathogenicity of R347Q, a mere catalytic mutation, and of L38P and A110Q mutations causing structural-functional defects. These are due to local perturbation transmitted to the active site, as predicted by molecular dynamic analyses. Overall, the results not only give comprehensive molecular insights into AADC deficiency, but also provide an experimental framework to suggest appropriate therapeutic treatments.

S250F variant associated with aromatic amino acid decarboxylase deficiency: molecular defects and intracellular rescue by pyridoxine.

Dopa or aromatic amino acid decarboxylase (DDC, AADC) is a pyridoxal 5'-phosphate-dependent enzyme that catalyses the production of the neurotransmitters dopamine and serotonin. Among the so far identified mutations associated with AADC deficiency, an inherited rare neurometabolic disease, the S250F mutation is the most frequent one. Here, for the first time, the molecular basis of the deficit of the S250F variant was investigated both in vitro and in cellular systems. Ser250 is not essential for the catalytic activity of the enzyme. However, its mutation to Phe causes a ~7-fold reduction of catalytic efficiency and a conformational change in the proximity of the mutated residue that is transmitted to the active site. In cellular extracts of E. coli and mammalian cells, both the specific activity and the protein level of the variant decrease with respect to the wild-type. The results with mammalian cells indicate that the mutation does not affect intracellular mRNA levels, and are consistent with a model where S250F undergoes a degradation process via the proteasome, possibly through an ubiquitination process occurring faster than in the wild-type. Overall, biochemical and cell biology experiments show that loss of function of S250F occurs by two distinct but not exclusive mechanisms affecting activity and folding. Importantly, 4-phenylbutirric acid (4-PBA) or, to a major extent, pyridoxine increase the expression level and, in a dose-dependent manner, the decarboxylase specific activity of mutant-expressing cells. This strongly suggests that 4-PBA and/or pyridoxine administration may be of important value in therapy of patients bearing the S250F mutation.

Harnessing inter-kingdom metabolic disparities at the human-fungal interface for novel therapeutic approaches.

Humans interact with a multitude of microorganisms in various ecological relationships, ranging from commensalism to pathogenicity. The same applies to fungi, long recognized for their pathogenic roles in infection-such as in invasive fungal diseases caused, among others, by Aspergillus fumigatus and Candida spp.-and, more recently, for their beneficial activities as an integral part of the microbiota. Indeed, alterations in the fungal component of the microbiota, or mycobiota, have been associated with inflammatory, infectious and metabolic diseases, and cancer. Whether acting as opportunistic pathogens or symbiotic commensals, fungi possess a complex enzymatic repertoire that intertwines with that of the host. In this metabolic cross-talk, fungal enzymes may be unique, thus providing novel metabolic opportunities to the host, or, conversely, produce toxic metabolites. Indeed, administration of fungal probiotics and fungi-derived products may be beneficial in inflammatory and infectious diseases, but fungi may also produce a plethora of toxic secondary metabolites, collectively known as mycotoxins. Fungal enzymes may also be homologues to human enzymes, but nevertheless embedded in fungal-specific metabolic networks, determined by all the interconnected enzymes and molecules, quantitatively and qualitatively specific to the network, such that the activity and metabolic effects of each enzyme remain unique to fungi. In this Opinion, we explore the concept that targeting this fungal metabolic unicity, either in opportunistic pathogens or commensals, may be exploited to develop novel therapeutic strategies. In doing so, we present our recent experience in different pathological settings that ultimately converge on relevant trans-kingdom metabolic differences.

Non-consecutive enzyme interactions within TCA cycle supramolecular assembly regulate carbon-nitrogen metabolism.

Enzymes of the central metabolism tend to assemble into transient supramolecular complexes. However, the functional significance of the interactions, particularly between enzymes catalyzing non-consecutive reactions, remains unclear. Here, by co-localizing two non-consecutive enzymes of the TCA cycle from Bacillus subtilis, malate dehydrogenase (MDH) and isocitrate dehydrogenase (ICD), in phase separated droplets we show that MDH-ICD interaction leads to enzyme agglomeration with a concomitant enhancement of ICD catalytic rate and an apparent sequestration of its reaction product, 2-oxoglutarate. Theory demonstrates that MDH-mediated clustering of ICD molecules explains the observed phenomena. In vivo analyses reveal that MDH overexpression leads to accumulation of 2-oxoglutarate and reduction of fluxes flowing through both the catabolic and anabolic branches of the carbon-nitrogen intersection occupied by 2-oxoglutarate, resulting in impeded ammonium assimilation and reduced biomass production. Our findings suggest that the MDH-ICD interaction is an important coordinator of carbon-nitrogen metabolism.

Dual species sphingosine-1-phosphate lyase inhibitors to combine antifungal and anti-inflammatory activities in cystic fibrosis: a feasibility study.

Cystic fibrosis (CF) is an autosomal recessive disorder characterized by respiratory failure due to a vicious cycle of defective Cystic Fibrosis Transmembrane conductance Regulator (CFTR) function, chronic inflammation and recurrent bacterial and fungal infections. Although the recent introduction of CFTR correctors/potentiators has revolutionized the clinical management of CF patients, resurgence of inflammation and persistence of pathogens still posit a major concern and should be targeted contextually. On the background of a network-based selectivity that allows to target the same enzyme in the host and microbes with different outcomes, we focused on sphingosine-1-phosphate (S1P) lyase (SPL) of the sphingolipid metabolism as a potential candidate to uniquely induce anti-inflammatory and antifungal activities in CF. As a feasibility study, herein we show that interfering with S1P metabolism improved the immune response in a murine model of CF with aspergillosis while preventing germination of Aspergillus fumigatus conidia. In addition, in an early drug discovery process, we purified human and A. fumigatus SPL, characterized their biochemical and structural properties, and performed an in silico screening to identify potential dual species SPL inhibitors. We identified two hits behaving as competitive inhibitors of pathogen and host SPL, thus paving the way for hit-to-lead and translational studies for the development of drug candidates capable of restraining fungal growth and increasing antifungal resistance.

Identification of Human Alanine-Glyoxylate Aminotransferase Ligands as Pharmacological Chaperones for Variants Associated with Primary Hyperoxaluria Type 1.

Primary hyperoxaluria type I (PH1) is a rare kidney disease due to the deficit of alanine:glyoxylate aminotransferase (AGT), a pyridoxal-5'-phosphate-dependent enzyme responsible for liver glyoxylate detoxification, which in turn prevents oxalate formation and precipitation as kidney stones. Many PH1-associated missense mutations cause AGT misfolding. Therefore, the use of pharmacological chaperones (PCs), small molecules that promote correct folding, represents a useful therapeutic option. To identify ligands acting as PCs for AGT, we first performed a small screening of commercially available compounds. We tested each molecule by a dual approach aimed at defining the inhibition potency on purified proteins and the chaperone activity in cells expressing a misfolded variant associated with PH1. We then performed a chemical optimization campaign and tested the resulting synthetic molecules using the same approach. Overall, the results allowed us to identify a promising hit compound for AGT and draw conclusions about the requirements for optimal PC activity.