Capturing protein structural kinetics by mass spectrometry

Precise knowledge of the three-dimensional structure of a protein is critical, if we are to understand its biological role and mode of action. However, today it is becoming increasingly clear that dissecting the protein's structural architecture is not enough: a complete description of biomolecular activity must also include the dimension of time. Protein motion and dynamics are crucial for protein stability and reactivity. A range of techniques have been developed for probing dynamic processes. In this tutorial review, we focus on one of these approaches - structural mass spectrometry (MS). MS has the ability to capture functional conformational transitions in the slow time regime, from a few milliseconds to hours. The power of this approach lies not only in its sensitivity and speed of analysis, but also in the fact that it is a non-ensemble technique. Thus, within a single spectrum, the entire distribution of co-existing states can be resolved. In discussing the challenges, advantages and limitations of the field, as well as future directions, we highlight the applicability of MS for quantitative monitoring of structural kinetics. In particular, we describe the array of MS-based strategies that are available for capturing protein folding, enzymatic reactions, ligand interactions, subunit exchange and biogenesis pathways.