Crystallography and NMR: Applications to Structural Biology

Abstract

Alongside X-ray crystallography, NMR plays an essential supporting role in structural biology in characterizing the structural and physical properties of proteins and other biological macromolecules. Approximately 15% of the ∼40 000 unique structures represented in the protein databank have been solved in solution using NMR methods. Yet, for various reasons, many proteins are not amenable to NMR analysis in solution and do not readily form diffracting crystals. A recent advance has arisen from a combination of new sample preparation procedures, sophisticated NMR pulse sequences, and instrumentation, collectively forming a new approach termed protein NMR crystallography. In this approach, multidimensional solid-state magic-angle spinning (MAS) NMR methods are used to extract structural and dynamic information from (usually soluble) proteins in hydrated precipitates that are ordered but nonetheless unsuitable for analysis by diffraction methods. This article introduces the main concepts and procedures that have emerged in this new but rapidly developing field and outlines some of the strategies and considerations for spectral assignment and three-dimensional structure determination. After several years of method validation with well-characterized proteins, NMR crystallography is now poised to provide the first de novo structures of proteins that have defied analysis by conventional techniques in structural biology.