The STINT-NMR method for studying in-cell protein-protein interactions.

This unit describes critical components and considerations required to study protein-protein structural interactions inside a living cell by using NMR spectroscopy (STINT-NMR). STINT-NMR entails sequentially expressing two (or more) proteins within a single bacterial cell in a time-controlled manner and monitoring their interactions using in-cell NMR spectroscopy. The resulting spectra provide a complete titration of the interaction and define structural details of the interacting surfaces at the level of single amino acid residues. The advantages and limitations of STINT-NMR are discussed, along with the differences between studying macromolecular interactions in vitro and in vivo (in-cell). Also described are considerations in the design of STINT-NMR experiments, focusing on selecting appropriate overexpression plasmid vectors, sample requirements and instrumentation, and the analysis of STINT-NMR data, with specific examples drawn from published works. Applications of STINT-NMR, including an in-cell methodology to post-translationally modify interactor proteins and an in-cell NMR assay for screening small molecule interactor libraries (SMILI-NMR) are presented.