Cardiolipin Modulates the Activity of the Intramembrane Protease GlpG Inducing Membrane Restructuring

Cardiolipin (CL) is a very important lipid in bacteria and the mitochondria of higher cells. CL is characterized by a unique structure, featuring four acyl chains and two negative charges, exhibiting a highly negative intrinsic curvature. We investigate the influence of CL on the function of the intramembrane E. coli protease GlpG, reconstituted into E. coli-like membranes. To underline the importance of CL, we find a ∼40% accelerated substrate cleavage rate in the presence of 10 mol % CL in phosphatidylethanolamine (PE)/phosphatidylglycerol (PG) membranes. CL induces a lateral restructuring of the membrane: without CL, PE/PG in the lipid annulus show a decreased chain length to match the hydrophobic thickness of GlpG. When CL is present, PE and PG share the properties of the bulk lipids, while CL undergoes the same amount of thinning that was observed for PE/PG before. To reveal the molecular properties of CL, we collect a multitude of NMR parameters to quantitatively describe the structure and dynamics of CL in the absence and presence of GlpG. In addition to the chain disordering and reduction of membrane thickness, we observe that some CL species follow the slow rotational diffusive motions of GlpG. This implies an association with GlpG, indicating preferential GlpG-CL interactions. We suggest that the high negative charge and the negative intrinsic curvature of CL are the main determinants of this remarkable behavior.