Subsecond Time-Resolved Mass Spectrometry in Dynamic Structural Biology

Life at the molecular level is a dynamic world, where the key players-proteins, oligonucleotides, lipids, and carbohydrates-are in a perpetual state of structural flux, shifting rapidly between local minima on their conformational free energy landscapes. The techniques of classical structural biology, X-ray crystallography, structural NMR, and cryo-electron microscopy (cryo-EM), while capable of extraordinary structural resolution, are innately ill-suited to characterize biomolecules in their dynamically active states. Subsecond time-resolved mass spectrometry (MS) provides a unique window into the dynamic world of biological macromolecules, offering the capacity to directly monitor biochemical processes and conformational shifts with a structural dimension provided by the electrospray charge-state distribution, ion mobility, covalent labeling, or hydrogen-deuterium exchange. Over the past two decades, this suite of techniques has provided important insights into the inherently dynamic processes that drive function and pathogenesis in biological macromolecules, including (mis)folding, complexation, aggregation, ligand binding, and enzyme catalysis, among others. This Review provides a comprehensive account of subsecond time-resolved MS and the advances it has enabled in dynamic structural biology, with an emphasis on insights into the dynamic drivers of protein function.

Co-solvent effects on reaction rate and reaction equilibrium of an enzymatic peptide hydrolysis

This work presents an approach that expresses the Michaelis constant KaM and the equilibrium constant K_th of an enzymatic peptide hydrolysis based on thermodynamic activities instead of concentrations.

An improved rapid mixing device for time-resolved electrospray mass spectrometry measurements

Time series data can provide valuable insight into the complexity of biological reactions. Such information can be obtained by mass-spectrometry-based approaches that measure pre-steady-state kinetics. These methods are based on a mixing device that rapidly mixes the reactants prior to the on-line mass measurement of the transient intermediate steps. Here, we describe an improved continuous-flow mixing apparatus for real-time electrospray mass spectrometry measurements. Our setup was designed to minimize metal–solution interfaces and provide a sheath flow of nitrogen gas for generating stable and continuous spray that consequently enhances the signal-to-noise ratio. Moreover, the device was planned to enable easy mounting onto a mass spectrometer replacing the commercial electrospray ionization source. We demonstrate the performance of our apparatus by monitoring the unfolding reaction of cytochrome C, yielding improved signal-to-noise ratio and reduced experimental repeat errors.

Flexibility and reactivity in promiscuous enzymes

Best of both worlds: The interplay of active site reactivity and the dynamic character of proteins allows enzymes to be promiscuous and--sometimes--remarkably efficient at the same time. This review analyses the roles structural flexibility and chemical reactivity play in the catalytic mechanism of selected enzymes.