Proteins undergo structural transitions and dynamically interact with one another to play critical physiological roles in living organisms. Understanding how these molecular machines work in detail is vital to promote our understanding of biology at molecular levels. However, the complex structures and rapid molecular motions make experimental investigations with proper spatial and temporal resolutions very challenging.
In this seminar, I will introduce a novel time-resolved solid-state NMR (ssNMR) technique based on a rapid mixer/freezer device that can initiate structural transitions within 1-2 milliseconds and freeze-trap intermediate states on the microsecond timescale after varying evolution times. A state-of-the-art NMR signal enhancement technique at cryogenic temperature, Dynamic Nuclear Polarization (DNP), is then implemented to characterize transient states during such a non-equilibrium kinetic process. I will discuss the details of these home-built instruments and their performances in terms of mixing/cooling rates and signal enhancement factors from DNP. I will then present results from the first two published applications of time-resolved ssNMR: (1) folding and self-assembly of an antimicrobial peptide, melittin; and (2) formation of complexes between the biologically essential calcium-sensor protein calmodulin and one of its target proteins, Myosin Light Chain Kinase (MLCK), in the presence of Ca2+. In both studies, a series of 2D ssNMR spectra at evolution times between 1.5 and 30 milliseconds provided unanticipated information about structural transitions and intermediate states at a site-specific level. Prospects for future applications and extensions of these methods will also be discussed.