Segmental labeling: Applications to protein NMR and DNP

Magic-angle spinning (MAS) NMR coupled with dynamic nuclear polarization (DNP) has the possibility to increase the sensitivity of MAS NMR by several orders of magnitude. While DNP enables many experiments that are sensitivity limited, such as those on dilute samples or those that measure long-range distances, interpretation of DNP NMR spectra is often limited by broad lines and chemical shift degeneracy. Segmental isotopic labeling using split intein technology can provide an opportunity to overcome this issue. Isotopic labeling of only a segment of a protein that is otherwise unlabeled reduces the chemical shift degeneracy. In this article, we describe the current state of the art for producing segmentally isotopically labeled proteins using split inteins. We discuss some of the potential applications of segmental isotopic labeling, particularly those that exploit the increased experimental sensitivity of DNP-enhanced MAS NMR spectroscopy.