Residual dipolar couplings in structure determination of biomolecules.

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Abstract

The use of residual dipolar couplings (RDCs) in the analysis of biomolecular structure and dynamics has expanded rapidly since its potential as a source of structural information on proteins was demonstrated in the mid 1990s.1,2 Of course, this work on proteins rested on applications to smaller biomolecular systems that occurred much earlier,3 and even these early applications benefited from prior research on organic molecules in partially ordered liquid crystals.4 However, in the 1990s, the existence of efficient means of introducing magnetically active isotopic labels (13C and 15N) and the availability of triple resonance strategies for selective manipulation and assignment of NMR resonances made widespread application to large biomolecules possible. It was fortuitous that the 13C and 15N labels introduced had small magnetogyric ratios, allowing simple dipolar interactions with directly bonded protons to dominate RDC observations. Prior work had focused on systems with couplings coming from the much larger 1H-1H dipolar and 2H quadrupolar interactions. While large interactions and the resultant increased size of observable couplings may have seemed an advantage, these large interactions also lead to complex spectra and broader lines. In the case of 1H1H interactions, additional splittings of resonances from protons at long distances arose, and in both cases broader lines resulted from enhanced spin relaxation processes. Since the recognition of the potential of RDCs in protein structure determination, applications have spread to nucleic acid structure, carbohydrate structure, protein-ligand interactions, protein domain relationships, high-throughput strategies for structural genomics, and studies of motional amplitudes in flexible assemblies. Related pieces of data coming from interactions with paramagnetic sites and chemical shift anisotropy (CSA) offsets have also come onto the scene. Each new application demands parallel improvements in sample preparation, data acquisition, and data analysis methods. The development of RDC applications has been reviewed periodically since their introduction to the structural biology field,5-13 and the reader is referred to these reviews for a more complete description of the history and the underlying theory. Here, we will provide a brief introduction to RDCs and related data as they are used today. Advances that have been made in alignment techniques, data acquisition techniques, and analysis methods will be reviewed. In the course of this review, we will provide examples of applications that use these methods. Applications, per se, have become too numerous to attempt a comprehensive review. * To whom correspondence should be addressed. James H. Prestegard, Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, GA, 30602. Phone: (706) 542-6281. Fax: (706) 542-4412. E-mail: jpresteg@ccrc.uga.edu. † University of Georgia. ‡ Institut de Biologie Structurale. 3519 Chem. Rev. 2004, 104, 3519−3540