Oral Presentation 23rd International Society of Magnetic Resonance Conference 2023

Experimental evidence from time-resolved solid-state NMR for millisecond structural annealing of the ultra-fast folding villin headpiece subdomain HP35 (#62)

Blake Wilson 1 , Wai-Ming Yau 1 , Robert Tycko 1
  1. National Institute of Diabetes and Digestive and Kidney Disseases, Bethesda, MARYLAND, United States

Kinetic experiments carried out after triggering a structural conversion can provide invaluable insights into folding mechanics, including the possibility of directly accessing short-lived intermediate or off-pathway states; however, combining sufficiently fast time resolution with techniques that provide detailed, atomic-scale spatial resolution is challenging. Time-resolved solid-state nuclear magnetic resonance (ssNMR) spectroscopy combines site-specific, atomistic structural information with millisecond time resolution by first triggering a conversion process, then taking "snapshots" of structural changes by rapidly freezing after a variable evolution delay [1]. In this work we use sub-millisecond negative temperature jumps to trigger folding of the 35-residue villin headpiece subdomain (HP35), an ultra-fast folding protein studied extensively and widely used as a folding benchmark. With a specially constructed temperature-jump apparatus utilizing copper capillary tubes anchored to temperature-controlled copper plates, solutions containing HP35 are first heated to 95 °C, causing HP35 to unfold, then rapidly cooled to 30 °C in 0.6 ms to trigger folding. After a variable evolution time at 30 °C, HP35 is frozen in ~0.15 ms in a -145 °C isopentane bath. Frozen ensembles are subsequently studied using magic angle spinning ssNMR enhanced with dynamic nuclear polarization (DNP), with experiments carried out at 25 K, 90 K, and 115 K. 1D and 2D ssNMR spectra acquired as a function of the variable evolution time show signals consistent with native secondary structure forming on the sub-millisecond timescale, as expected from previous studies, but crucially provide evidence that full structural order, including alignment of native sidechain configurations, forms much slower through a millisecond structural annealing process. ssNMR provides the quantitative, site-specific, and atomistic information necessary to characterize this annealing process, which has not been previously observed in ultra-fast folding proteins. Time-resolved ssNMR triggered by rapid temperature jumps offers direct access to short-lived structures and complexes and is applicable to diverse biomolecular and biophysical systems.

  1. [1] Jeon, Wilson, Yau, Thurber, Tycko, "Time-resolved solid state NMR of biomolecular processes with millisecond time resolution," Journal of Magnetic Resonance, Vol. 342, 107285 (2022)