Development of a microfluidic confocal fluorescence detection system for the hyphenation of nano-LC to on-line biochemical assays

One way to profile complex mixtures for receptor affinity is to couple liquid chromatography (LC) on-line to biochemical detection (BCD). A drawback of this hyphenated screening approach is the relatively high consumption of sample, receptor protein and (fluorescently labeled) tracer ligand. Here, we worked toward minimization of sample and reagent consumption, by coupling nano-LC on-line to a light-emitting diode (LED) based capillary confocal fluorescence detection system capable of on-line BCD with low-flow rates. In this fluorescence detection system, a capillary with an extended light path (bubble cell) was used as a detection cell in order to enhance sensitivity. The technology was applied to a fluorescent enhancement bioassay for the acetylcholine binding protein, a structural analog of the extracellular ligand-binding domain of neuronal nicotinic acetylcholine receptors. In the miniaturized setup, the sensitive and low void volume LED-induced confocal fluorescence detection system operated in flow injection analysis mode allowing the measurement of IC(50) values, which were comparable with those measured by a conventional plate reader bioassay. The current setup uses 50 nL as injection volume with a carrier flow rate of 400 nL/min. Finally, coupling of the detection system to gradient reversed-phase nano-LC allowed analysis of mixtures in order to identify the bioactive compounds present by injecting 10 nL of each mixture

Fragment library screening reveals remarkable similarities between the G protein-coupled receptor histamine H4 and the ion channel serotonin 5-HT3A

A fragment library was screened against the G protein-coupled histamine H4 receptor (H4R) and the ligand-gated ion channel serotonin 5-HT3A (5-HT3AR). Interestingly, significant overlap was found between H4R and 5-HT3AR hit sets. The data indicates that dual active H4R and 5 HT3AR fragments have a higher complexity than the selective compounds which has important implications for chemical genomics approaches. The results of our fragment-based library screening study illustrate similarities in ligand recognition between H4R and 5-HT3AR and have important consequences for selectivity profiling in ongoing drug discovery efforts on H4R and 5-HT3AR. The affinity profiles of our fragment screening studies furthermore match the chemical properties of the H4R and 5-HT3AR binding sites and can be used to define molecular interaction fingerprints to guide the in silico prediction of protein-ligand interactions and structure