RESUMEN
In-cell NMR spectroscopy is an effective tool for observing proteins at atomic resolution in their native cellular environment. However, its utility is limited by its low sensitivity and the extensive line broadening caused by nonspecific interactions in the cells, which is even more pronounced in human cells due to the difficulty of overexpressing or delivering high concentrations of isotopically labeled proteins. Here, we present a high-sensitivity tag (wPSP-6F) containing two trifluoromethyl groups that can efficiently label globular proteins with molecular weights in the 6-40â kDa range under mild conditions. This tag allowed us to detect globular proteins in human cells at concentrations as low as 1.0â µM, which would not have been achievable with 15 N or 3-fluorotyrosine labeling. Moreover, we detected conformational changes and interactions of proteins in the cellular environment. The new sensitive 19 F NMR tag may significantly expand the scope of protein NMR in human cells.
Asunto(s)
Imagen por Resonancia Magnética , Proteínas , Humanos , Proteínas/química , Espectroscopía de Resonancia Magnética/métodos , Resonancia Magnética Nuclear Biomolecular/métodosRESUMEN
Labeling and visualizing cells and subcellular structures within thick tissues, whole organs, and even intact animals is key to studying biological processes. This is particularly true for studies of neural circuits where neurons form submicron synapses but have arbors that may span millimeters in length. Traditionally, labeling is achieved by immunofluorescence; however, diffusion of antibody molecules (>100 kDa) is slow and often results in uneven labeling with very poor penetration into the center of thick specimens; these limitations can be partially addressed by extending staining protocols to over a week (Drosophila brain) and months (mice). Recently, we developed an alternative approach using genetically encoded chemical tags CLIP, SNAP, Halo, and TMP for tissue labeling; this resulted in >100-fold increase in labeling speed in both mice and Drosophila, at the expense of a considerable drop in absolute sensitivity when compared to optimized immunofluorescence staining. We now present a second generation of UAS- and LexA-responsive CLIPf, SNAPf, and Halo chemical labeling reagents for flies. These multimerized tags, with translational enhancers, display up to 64-fold increase in sensitivity over first-generation reagents. In addition, we developed a suite of conditional reporters (4xSNAPf tag and CLIPf-SNAPf-Halo2) that are activated by the DNA recombinase Bxb1. Our new reporters can be used with weak and strong GAL4 and LexA drivers and enable stochastic, intersectional, and multicolor Brainbow labeling. These improvements in sensitivity and experimental versatility, while still retaining the substantial speed advantage that is a signature of chemical labeling, should significantly increase the scope of this technology.
Asunto(s)
Drosophila/citología , Imagen Óptica/métodos , Coloración y Etiquetado/métodos , Transferasas Alquil y Aril/genética , Transferasas Alquil y Aril/metabolismo , Animales , Encéfalo/citología , Encéfalo/metabolismo , Drosophila/genética , Drosophila/metabolismo , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Colorantes Fluorescentes/química , Microscopía Fluorescente/métodos , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Sensibilidad y EspecificidadRESUMEN
This review focuses on the various approaches to covalently attach a chromophore to a biomolecule of interest in site-specific manner. Novel methods like inverse electron-demand Diels-Alder reaction, Pictet-Spengler ligation and enzyme tags like SNAP and Halo-tags are critically discussed and compared to established techniques like copper-free click reaction and native chemical ligation. Selected examples in which the tags have been exploited for in vitro or in vivo imaging are reviewed and evaluated.