Abstract: Solid-state nuclear magnetic resonance (SSNMR) has recently emerged as a unique spectroscopic tool, with great potential for providing atomic-resolution images of biomacromolecules that are not amenable to characterization by traditional high-resolution methods. I will discuss the basics of biomolecular magic-angle spinning SSNMR spectroscopy and describe our recent studies aimed at the detailed characterization of amyloid aggregates formed by the Y145Stop mutant of prion protein (PrP).^1,2 This particular PrP variant is associated with the development of a heritable cerebral amyloidosis in humans, and, importantly, has been shown to provide an experimentally-tractable in vitro model for investigating the phenomena of prion strains and transmissibility barriers in mammalian prion propagation. If time permits, I will also describe our recent SSNMR studies of natively diamagnetic proteins intentionally modified with paramagnetic tags, including nitroxide spin labels and transition metal ions.^3,4 The primary aim of these studies is to develop novel SSNMR methodologies that exploit the nuclear paramagnetic relaxation enhancement (PRE) phenomenon to obtain long-range (up to ~20 Å) structural restraints inaccessible to conventional SSNMR methods, and to eventually utilize these PRE restraints for de novo SSNMR protein structure refinement.

1. J.J. Helmus, K. Surewicz, P.S. Nadaud, W.K. Surewicz, C.P. Jaroniec, Proc. Natl. Acad. Sci. USA 2008, 105, 6284-6289.
2. J.J. Helmus, K. Surewicz, W.K. Surewicz, C.P. Jaroniec, J. Am. Chem. Soc. 2010, 132, 2393-2403.
3. P.S. Nadaud, J.J. Helmus, N. Höfer, C.P. Jaroniec, J. Am. Chem. Soc. 2007, 129, 7502-7503.
4. P.S. Nadaud, J.J. Helmus, S.L. Kall, C.P. Jaroniec, J. Am. Chem. Soc. 2009, 131, 8108-8120.

Abstract: Reductive methylation of lysine residues permitted the introduction of ¹³C-labels in samples of β2 adrenergic receptor – a member of an important class of drug discovery targets - the G protein coupled receptors. Indirect detection of ¹³C-methylated lysine residues enabled monitoring of ligand-induced modulations of the salt bridge between lys305 & asp192 at the interface of the extra-cellular loops 2 & 3. This salt bridge contributes to the formation of a cavity on the extra cellular surface of the receptor. The extra-cellular surface adjacent to this NMR-detectable K305 : D192 salt bridge may be amenable to the design of subtype-specific exosite modulators of β2 AR activity, and may prove an attractive venue for overcoming the challenge of designing subtype specific β2 AR modulators. Distinction between highly mobile and structurally restrained lysine methyls was achieved via saturation transfer filtered hc hmqc and hc hsqc experiments.