Probing Structural and Motional Features of the C‑Terminal Part of the Human Centrin 2/P17-XPC Microcrystalline Complex by Solid- State NMR Spectroscopy

*S Supporting Information ABSTRACT: Insight into structural and motional features of the C-terminal part of the Human Centrin 2 in complex with the peptide P17-XPC was obtained by using complementary solid-state NMR methods. We demonstrate that the experimental conditions and procedures of sample crystallization determine the quality of solid-state NMR spectra and the internal mobility of the protein. Two-dimensional (2D) 13C−13C and 15N−15N correlation spectra reveal intra- and inter-residue dipolar connectivities and provide partial, site-specific assignments of 13C and 15N resonance signals. The secondary structure of the C-ter HsCen2/P17-XPC complex in a microcrystalline state appears similar to that found in solution. Conformational flexibility is probed through relaxation-compensated measurements of dipolar order parameters that exploit the dynamics of cross-polarization in multidimensional experiments. The extracted dipolar coupling constants and relevant order parameters reveal increased backbone flexibility of the loops except for residues involved in coordination with the Ca2+ cation that stabilizes the hydrophobic pocket containing the peptide P17-XPC. 1