Tailoring the Specificity and Reactivity of a Mechanism-Based Inactivator of Glucocerebrosidase for Potential Therapeutic Applications

Iminosugar-Dihydroazulenes as Mutant L444P Glucocerebrosidase Enhancers

A remarkable enhancer of human glucocerebrosidase enzyme (GCase) was identified among a set of dihydroazulene-tagged iminosugars. An unprecedented 3.9-fold increase in GCase activity was detected on fibroblasts bearing the homozygous L444P mutation, which is frequently associated with neuronopathic Gaucher forms, and which commonly results refractory to chaperone-induced refolding.

Spatial Chemoproteomics for Mapping the Active Proteome

Functional regulation of cell signaling through dynamic changes in protein activity state as well as spatial organization represent two dynamic, complex, and conserved phenomena in biology. Seemingly separate areas of -omics method development have focused on building tools that can detect and quantify protein activity states, as well as map sub-cellular and intercellular protein organization. Integration of these efforts, through the development of chemical tools and platforms that enable detection and quantification of protein functional states with spatial resolution provide opportunities to better understand heterogeneity in the proteome within cell organelles, multi-cellular tissues, and whole organisms. This review provides an overview of and considerations for major classes of chemical proteomic probes and technologies that enable protein activity mapping from sub-cellular compartments to live animals.

Lipid-mimicking phosphorus-based glycosidase inactivators as pharmacological chaperones for the treatment of Gaucher's disease

Gaucher's disease, the most prevalent lysosomal storage disorder, is caused by missense mutation of the GBA gene, ultimately resulting in deficient GCase activity, hence the excessive build-up of cellular glucosylceramide. Among different therapeutic strategies, pharmacological chaperoning of mutant GCase represents an attractive approach that relies on small organic molecules acting as protein stabilizers. Herein, we expand upon a new class of transient GCase inactivators based on a reactive 2-deoxy-2-fluoro-β-d-glucoside tethered to an array of lipid-mimicking phosphorus-based aglycones, which not only improve the selectivity and inactivation efficiency, but also the stability of these compounds in aqueous media. This hypothesis was further validated with kinetic and cellular studies confirming restoration of catalytic activity in Gaucher cells after treatment with these pharmacological chaperones.

Fluorinated carbohydrates as chemical probes for molecular recognition studies. Current status and perspectives

This review provides an extensive summary of the effects of carbohydrate fluorination with regard to changes in physical, chemical and biological properties with respect to regular saccharides. The specific structural, conformational, stability, reactivity and interaction features of fluorinated sugars are described, as well as their applications as probes and in chemical biology.

Stabilization of Glucocerebrosidase by Active Site Occupancy

Glucocerebrosidase (GBA) is a lysosomal β-glucosidase that degrades glucosylceramide. Its deficiency results in Gaucher disease (GD). We examined the effects of active site occupancy of GBA on its structural stability. For this, we made use of cyclophellitol-derived activity-based probes (ABPs) that bind irreversibly to the catalytic nucleophile (E340), and for comparison, we used the potent reversible inhibitor isofagomine. We demonstrate that cyclophellitol ABPs improve the stability of GBA in vitro, as revealed by thermodynamic measurements (T_m increase by 21 °C), and introduce resistance to tryptic digestion. The stabilizing effect of cell-permeable cyclophellitol ABPs is also observed in intact cultured cells containing wild-type GBA, N370S GBA (labile in lysosomes), and L444P GBA (exhibits impaired ER folding): all show marked increases in lysosomal forms of GBA molecules upon exposure to ABPs. The same stabilization effect is observed for endogenous GBA in the liver of wild-type mice injected with cyclophellitol ABPs. Stabilization effects similar to those observed with ABPs were also noted at high concentrations of the reversible inhibitor isofagomine. In conclusion, we provide evidence that the increase in cellular levels of GBA by ABPs and by the reversible inhibitor is in part caused by their ability to stabilize GBA folding, which increases the resistance of GBA against breakdown by lysosomal proteases. These effects are more pronounced in the case of the amphiphilic ABPs, presumably due to their high lipophilic potential, which may promote further structural compactness of GBA through hydrophobic interactions. Our study provides further rationale for the design of chaperones for GBA to ameliorate Gaucher disease.

Fungal Glycolipid Hydrolase Inhibitors and Their Effect on Cryptococcus neoformans

Pathogenic fungi kill an estimated 1.3 million people each year. This number is predicted to rise as drug resistance spreads, thus antifungal drugs with novel modes of action are urgently required. Fungal endoglycoceramidase-related proteins 1 and 2 (EGCrP-1 and -2), which hydrolyse glucosylceramide and ergosteryl β-glucoside, respectively, are important for fungal cell growth and have been identified as potential targets for drug development. A library of iminosugar derivatives was screened against EGCrP-1 and -2, and a number of competitive inhibitors with nanomolar affinities were identified. In addition, a mechanism-based inhibitor was shown to form a covalent derivative with EGCrP-2. Nine of the inhibitors were evaluated against Cryptococcus neoformans. Several showed growth inhibitory activity, but only against a C. neoformans strain lacking the outer fungal polysaccharide capsule; this implies that penetration into the cell is a significant handicap for these inhibitors. Pro-drug versions of these inhibitors could address this issue.

pH-Responsive Pharmacological Chaperones for Rescuing Mutant Glycosidases

A general approach is reported for the design of small-molecule competitive inhibitors of lysosomal glycosidases programmed to 1) promote correct folding of mutant enzymes at the endoplasmic reticulum, 2) facilitate trafficking, and 3) undergo dissociation and self-inactivation at the lysosome. The strategy is based on the incorporation of an orthoester segment into iminosugar conjugates to switch the nature of the aglycone moiety from hydrophobic to hydrophilic in the pH 7 to pH 5 window, which has a dramatic effect on the enzyme binding affinity. As a proof of concept, new highly pH-responsive glycomimetics targeting human glucocerebrosidase or α-galactosidase with strong potential as pharmacological chaperones for Gaucher or Fabry disease, respectively, were developed.

N-Alkylated aziridines are easily-prepared, potent, specific and cell-permeable covalent inhibitors of human β-glucocerebrosidase

N-Octyl conduritol aziridine is a potent and specific covalent inactivator of β-glucocerebrosidase (GBA1) inside live human cells.

Phosphodiesters serve as potentially tunable aglycones for fluoro sugar inactivators of retaining β-glycosidases

2-Deoxy-2-fluoroglycosides were synthesised and tested as covalent glycosidase inactivators. β-d-Gluco-, -manno- and -galacto-configured benzyl-benzylphosphonate derivatives efficiently inactivate β-gluco-, β-manno- and β-galactosidases, while α-gluco- and α-manno-configured phosphate and phosphonate derivatives instead served as slow substrates for their cognate α-glycosidases.

Tetrafluorination of sugars as strategy for enhancing protein-carbohydrate affinity: application to UDP-Galp mutase inhibition

Tetrafluorinated analogues of both UDP-galactopyranose and UDP-galactofuranose have been synthesized and assayed against UDP-galactopyranose mutase, a key enzyme for Mycobacterium tuberculosis cell wall biosynthesis. Competition assays and STD-NMR spectroscopy techniques have evidenced not only the first unambiguous case of affinity enhancement through local sugar polyfluorination, but also showed that tetrafluorination can still have a beneficial effect on binding when monofluorination at the same position does not.

Novel activity-based probes for broad-spectrum profiling of retaining β-exoglucosidases in situ and in vivo

A high-end label: Cyclophellitol aziridine-type activity-based probes allow for ultra-sensitive visualization of mammalian β-glucosidases (GBA1, GBA2, GBA3, and LPH) as well as several non-mammalian β-glucosidases (see picture). These probes offer new ways to study β-exoglucosidases, and configurational isomers of the cyclophellitol aziridine core may give activity-based probes targeting other retaining glycosidase families.