Solid-State NMR Provides Evidence for Small-Amplitude Slow Domain Motions in a Multispanning Transmembrane α-Helical Protein

• DOI: 10.1021/jacs.7b03974
• Publication Date: 2017-06-14T18:02:36Z
• Authors: Daryl Good; Charlie Pham; Jacob Jagas; Józef R. Lewandowski; Vladimir Ladizhansky
• Keywords: Nanosecond; Helix (gastropod); Picosecond; Protein Dynamics

Proteins are dynamic entities and populate ensembles of conformations. Transitions between states within a conformational ensemble occur over broad spectrum amplitude time scales, often related to biological function. Whereas solid-state NMR (SSNMR) spectroscopy has recently been used characterize proteins in the microcrystalline states, its applications membrane remain limited. Here we use SSNMR study dynamics seven-helical transmembrane (TM) protein, Anabaena Sensory Rhodopsin (ASR) reconstituted lipids. We report on site-specific measurements 15N longitudinal R1 rotating frame R1ρ relaxation rates at two fields 600 800 MHz temperatures 7 30 °C. Quantitative analysis values their field temperature dependencies provides evidence motions least scales. modeled these as fast local slower collective TM helices structured loops, simple model-free extended analyses fit data estimate amplitudes, scales activation energies. Faster picosecond (tens hundreds picoseconds) throughout protein dominant middle portions helices. In contrast, amplitudes occurring nanosecond nanoseconds) smaller central parts helices, but increase toward cytoplasmic sides well interhelical loops. ASR interacts with soluble transducer surface, binding affinity is modulated by light. The larger side correlates ability undergo large changes process binding/unbinding transducer.