Amino acid side chains involved in hydrogen bonds and electrostatic interactions are crucial for protein function. However, detailed investigations of such side chains in solution are rare. Here, through the combination of long-range 15N-13C scalar J-coupling measurements and an atomic-detail molecular dynamics (MD) simulation, direct insight into the structural dynamic behavior of lysine side chains in human ubiquitin has been gained. On the basis of 1H/13C/15N heteronuclear correlation experiments selective for lysine NH3 + groups, we analyzed two different types of long-range 15N-13C J-coupling constants: one between intraresidue 15Nζ and 13CCγ nuclei (3J NζCCγ) and the other between 15Nζ and carbonyl 13C′ nuclei across a hydrogen bond ( h3JNζC′). The experimental 3J NζCCγ data confirm the highly mobile nature of the Ξ4 torsion angles of lysine side chains seen in the MD simulation. The NH3+ groups of Lys29 and Lys33 exhibit measurable h3JNζC′ couplings arising from hydrogen bonds with backbone carbonyl groups of Glu16 and Thr14, respectively. When interpreted together with the 3JNζCCγ-coupling constants and NMR-relaxation-derived S2 order parameters of the NH 3+ groups, they strongly suggest that hydrogen bonds involving NH3+ groups are of a transient and highly dynamic nature, in remarkably good agreement with the MD simulation results.
ASJC Scopus subject areas
- Colloid and Surface Chemistry