Observing A Protein In Its Natural Habitat

Much of our knowledge about proteins inside biological cells comes from ex situ methods, where cellular proteins are extracted from their native environment. This approach has yielded basic information on each protein's structure and function averaged across distinct subcellular compartments, cell states, and, sometimes, cell types. However, the functional demands from different (sub)cellular environments vary. To probe the structural and functional adaptation of proteins in distinct subcellular environments, in situ single-protein characterization has emerged as an important approach. Here we comment on emerging in situ approaches by light and electron microscopy that begin to raise new questions about the distribution, structure, and function of individual protein copies in specific subcellular environments. The advent of in situ single-protein characterization is a key frontier of spatial biology to elucidate the architecture of a single cell.