¹⁵N-filtered, ¹³C-detected spin-correlations in solid-state NMR of macroscopically oriented samples

Oriented-sample (OS) solid-state NMR spectroscopy provides direct access to angular-dependent observables in membrane proteins macroscopically aligned in lipid bilayers, but has historically been limited to single-site detection, most commonly ¹⁵N amide sites, and lacks efficient multidimensional spectroscopic assignment strategies. Here we present a ¹⁵N-filtered, ¹³C-detected correlation experiment that enables site-resolved ¹³C'-¹⁵N-¹³C_α connectivity mapping for membrane proteins in macroscopically aligned samples. The method combines ¹⁵N editing and cross polarization transfer under ¹⁵N/¹³C spin-lock to establish nearest-neighbor and, potentially, two-bond correlations across peptide planes. Direct detection on the ¹³C channel combined with ¹⁵N filtering efficiently suppresses lipid background signals in uniformly labeled samples. Experiments on a model NAL single crystal and on Pf1 coat protein reconstituted in magnetically aligned bicelles demonstrate the appearance of multi-peak correlation patterns per ¹⁵N amide site, thereby reflecting both nearest-neighbor and two-bond polarization transfer pathways. This approach advances OS NMR from a purely orientational, single-site probe to a triple-resonance spectroscopic technique capable of encoding both angular restraints and backbone connectivity, thereby putting it on par with the more established MAS NMR techniques.