Local and Global Dynamics in Klebsiella pneumoniae Outer Membrane Protein a in Lipid Bilayers Probed at Atomic Resolution

The role of membrane proteins in cellular mechanism strongly depends on their dynamics, and solid-state magic-angle spinning (MAS) nuclear magnetic resonance (NMR) is a unique method to exhaustively characterize motions of proteins in a lipid environment. Herein, we make use of advances in 1H-detected MAS NMR to describe the dynamics of the membrane domain of the Outer membrane protein A of Klebsiella pneumoniae (KpOmpA). By measuring 1H–15N dipolar-coupling as well as 15N R1 and R1ρ relaxation rates at fast (60 kHz) MAS and high magnetic field (1 GHz), we were able to describe the motions of the residues of the β-barrel as a collective rocking of low amplitude and of hundreds of nanoseconds time scale. Residual local motions at the edges of the strands, underscored by enhanced 15N R1ρ relaxation rates, report on the mobility of the connected loops. In agreement with MAS NMR data, proteolysis experiments performed on the full length KpOmpA as well as on its membrane domain, reconstituted in liposomes or i...