Structure and Dynamics of the Rhomboid Protease GlpG in Liposomes Studied by Solid-State NMR

Rhomboid proteases are intramembrane proteases that hydrolyze substrate peptide bonds within the lipid bilayer and are important for a wide range of biological processes. The bacterial intramembrane protease GlpG is one of the model systems for structural investigations of the rhomboid family. Two different models of substrate gating have been proposed, based on crystal structures of GlpG in detergent micelles. Here, we present a detailed investigation of enzymatically active GlpG in a native-like lipid environment using solid-state NMR spectroscopy. Proton-detected experiments confirm the presence of water molecules in the catalytic cavity. A secondary chemical shift analysis indicates a previously unobserved kink in the central part of the gating helix TM5. Dynamics measurements revealed a dynamic hotspot of GlpG at the N-terminal part of TM5 and the adjacent loop L4, indicating that this region is important for gating. In addition, relaxation dispersion experiments suggest that TM5 is in conformational exchange between an open and a closed conformation.