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

Abstract

The role of membrane proteins in cellular mechanisms strongly depends on their dynamics; 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 motion of the β-barrel as a collective rocking of low amplitude and of hundreds of nano-seconds 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 in detergent micelles, revealed in all cases the existence of a unique Trypsin cleavage site within the membrane domain (out of 16 potential Lys and Arg sites). This site is located in the extracellular loop L3, indicating that this loop may be highly accessible to protein-protein interactions. KpOmpA is involved in cell-cell recognition, adhesion and immune response mechanisms. The L3 region may therefore play a key role in pathogenicity.