Introduction to the Minireview Series on Modern Technologies for In-cell Biochemistry.

The last decade has seen enormous progress in the exploration and understanding of the behavior of molecules in their natural cellular environments at increasingly high spatial and temporal resolution. Advances in microscopy and the development of new fluorescent reagents as well as genetic editing techniques have enabled quantitative analysis of protein interactions, intracellular trafficking, metabolic changes, and signaling. Modern biochemistry now faces new and exciting challenges. Can traditionally "in vitro" experiments, e.g. analysis of protein folding and conformational transitions, be done in cells? Can the structure and behavior of endogenous and/or non-tagged recombinant proteins be analyzed and altered within the cell or in cellular compartments? How can molecules and their actions be studied mechanistically in tissues and organs? Is personalized cellular biochemistry a reality? This thematic series summarizes recent studies that illustrate some first steps toward successfully answering these modern biochemical questions. The first minireview focuses on utilization of three-dimensional primary enteroids and organoids for mechanistic studies of intestinal biology with molecular resolution. The second minireview describes application of single chain antibodies (nanobodies) for monitoring and regulating protein dynamics in vitro and in cells. The third minireview highlights advances in using NMR spectroscopy for analysis of protein folding and assembly in cells.