An on-demand, drop-on-drop method for studying enzyme catalysis by serial crystallography

Currently many of the time resolved serial femtosecond (SFX) crystallography experiments are done with light driven protein systems, whereas the reaction initiation for non-light triggered enzymes remains a major bottle neck. Here, the authors present an expanded Drop-on-Tape system, where picoliter-sized droplets of a substrate or inhibitor are turbulently mixed with nanoliter sized droplets of microcrystal slurries, and they use it for time-resolved SFX measurements of inhibitor binding to lysozyme and secondly, binding of a β-lactam antibiotic to a bacterial serine β-lactamase.