Title: Probing allosteric coupling and dynamics with solid-state NMR
Description: Solid-state NMR (ssNMR) has matured into a versatile method to provide structural information, probe protein dynamics and detect small molecule binding and -protein interaction of a variety of biomolecular assemblies including amyloid fibrils, viral particles and membrane proteins. Membrane proteins embedded in liposomes are natural targets for ssNMR as their native states are solids. Magic angle spinning (MAS) ssNMR studies using moderate spinning frequencies provide detailed structural information and probe subtle conformational change. Development of fast magic angle spinning ssNMR enables proton-detection which increases sensitivity and facilitates protein dynamics measurements. In this dissertation, we applied moderate and fast MAS ssNMR to study potassium ion channel and protein dynamics Chapter 1 will introduce concepts and theory of solid-state NMR pulse sequences and experiments. Chapter 2 will discuss the application and perspectives of solid-state NMR to membrane protein systems.

In Chapter 3, we test an allostery mechanism for inactivation using a KcsA mutant (H25R/E118A) that exhibits an open pH gate across a broad range of pH values. We present solid-state NMR measurements of this open mutant at neutral pH to probe the affinity for potassium at the selectivity filter. This result strongly supports our assertion that the open pH gate allosterically affects the potassium binding affinity of the selectivity filter. In this mutant the protonation state of a glutamate residue (E120) in the pH sensor is sensitive to potassium binding, suggesting that this mutant also has flexibility in the activation gate and is subject to transmembrane allostery. In Chapter 4, I optimize protein expression, purification and reconstitution into native environment protocols of a bacterial potassium transporter, KtrB. In chapter 5, methods and experimental details of setting up 60 and 40 kHz fast MAS ssNMR are discussed. With fast MAS ssNMR setup, multidimensional NMR experiments with higher sensitivity could be collected on a perdeuterated sample with less sample mass required.

In Chapter 6, we employ fast MAS ssNMR to measure bulk and residue site-specific 15N and carbonyl 13C relaxation of microcrystalline ubiquitin. Carbonyl R1ρ relaxation profiles provide additional information on protein backbone dynamics.