Signature of Mobile Hydrogen Bonding of Lysine Side Chains from Long-Range ~(15)N-~(13)C Scalar J-Couplings and Computation

摘要

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 ~(15)N-~(13)C scalar/-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/~(13)C/~(15)N heteronuclear correlation experiments selective for lysine NH+3~+ groups, we analyzed two different types of long-range ~(15)N-~(13)C J-coupling constants: one between intraresidue ~(15)Nζand ~(13)Cγ nuclei (~3Jnζcγ) and the other between ~(15)Nζ and carbonyl ~(13)C' nuclei across a hydrogen bond (~h3Jnζc).The experimental 3Jnζcγ data confirm the highly mobile nature of the χ4 torsion angles of lysine side chains seen in the MD simulation. The NH_3~+ groups of Lys29 and Lys33 exhibit measurable ~h3Jnζc couplings arising from hydrogen bonds with backbone carbonyl groups of Glul6 and Thrl4, respectively. When interpreted together with the ~3Jnζcγ-coupling constants and NMR-relaxation-derived S~2 order parameters of the NH_3~+ groups, they strongly suggest that hydrogen bonds involving NH_3 groups are of a transient and highly dynamic nature, in remarkably good agreement with the MD simulation results.