DNA origami signposts for identifying proteins on cell membranes by electron cryotomography

Summary

Electron cryotomography (cryoET), an electron cryomicroscopy (cryoEM) modality, has changed our understanding of biological function by revealing the native molecular details of membranes, viruses, and cells. However, identification of individual molecules within tomograms from cryoET is challenging because of sample crowding and low signal-to-noise ratios. Here, we present a tagging strategy for cryoET that precisely identifies individual protein complexes in tomograms without relying on metal clusters. Our method makes use of DNA origami to produce “molecular signposts” that target molecules of interest, here via fluorescent fusion proteins, providing a platform generally applicable to biological surfaces. We demonstrate the specificity of signpost origami tags (SPOTs) in vitro as well as their suitability for cryoET of membrane vesicles, enveloped viruses, and the exterior of intact mammalian cells.

Graphical Abstract

Highlights

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  Asymmetric DNA signpost origami tags (SPOTs) precisely localize proteins

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  SPOTs identify specific proteins in electron cryomicroscopy

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  SPOTs have a high contrast “sign” and functionalized “post” base for targeting

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  SPOTs recognize fluorescent fusion proteins on vesicles, viruses, and cell surfaces

Abstract

Large, folded DNA structures, designed to recognize proteins on cell surfaces, facilitate in situ structural analyses.