Ligand-Directed Chemistry on Glycoside Hydrolases – A Proof of Concept Study

Selective covalent labelling of enzymes using small molecule probes has advanced the scopes of protein profiling. The covalent bond formation to a specific target is the key step of activity-based protein profiling (ABPP), a method which has become an indispensable tool for measuring enzyme activity in complex matrices. With respect to carbohydrate processing enzymes, strategies for ABPP so far involve labelling the active site of the enzyme, which results in permanent loss of activity. Here, we report in a proof of concept study the use of ligand-directed chemistry (LDC) for labelling glycoside hydrolases near – but not in – the active site. During the labelling process, the competitive inhibitor is cleaved from the probe, departs the active site and the enzyme maintains its catalytic activity. To this end, we designed a building block synthetic concept for small molecule probes containing iminosugar-based reversible inhibitors for labelling of two model β-glucosidases. The results indicate that the LDC approach can be adaptable for covalent proximity labelling of glycoside hydrolases.T. M. W. thanks the FWF (Wien, Austria) for financial support (project number P30372-B21). Authors from TU Graz acknowledge support from NAWI Graz.Peer reviewe

The Amadori rearrangement as glycoconjugation method: Synthesis of non-natural C-glycosyl type glycoconjugates

The Amadori rearrangement was investigated as a potential method for the conjugation of carbohydrate moieties to suitable amino components. Starting from selected aldoheptoses, which are readily available by means of the Kiliani–Fischer C-elongation reaction of the corresponding aldohexoses, glycoconjugates presenting D-gluco, D-manno and D-galacto as well as GlcNAc motifs have been synthesised. Following this strategy, non-natural C-glycosyl type glycoconjugates, which can be utilised as building blocks for the composition of larger molecular constructions, are available by a very short synthetic approach

Fluorescent-tagged sp2-iminosugars with potent β-glucosidase inhibitory activity

7 páginas, 3 figuras, 1 tablaNew fluorescently-labelled sp2-iminosugars based on the 5N,6S-[N′-(4-aminobutyl)iminomethylidene]-6-thionojirimycin skeleton have been synthesized as photoprobes to monitor glycosidase binding. Dansyl, dapoxyl and coumarin fluorophores were appended to the terminal amino group at the N′-substituent by either sulfonamide or amide bridging reaction. All the conjugates behaved as strong (low micromolar to nanomolar) and selective inhibitors of β-glucosidases (almonds and bovine liver) and naringinase, in agreement with the inhibition pattern previously encountered for related iso(thio)urea-type bicyclic sp2-iminosugars. The presence of the fluorescent probe allows real-time and continuous monitoring of β-glucosidase inhibition by fluorescence resonance energy transfer (FRET), taking advantage of the intrinsic tryptophan-associated fluorescence of the protein.The Spanish Ministerio de Ciencia e Innovación (contract numbers CTQ2006-15515-CO2-01, CTQ2009-14551-C02-01 and CTQ2007-61180/PPQ; cofinanced with the Fondo Europeo de Desarrollo Regional FEDER), the Spanish Ministerio de Educación (joint Austrian-Spanish action number HU2007-0006), the Fundación Ramón Areces, and the Junta de Andalucía are thanked for funding. M.A.-M. is a FPU doctoral fellow holder.Peer reviewe