Mass Spectrometry of Bacterial Outer Membrane Enzymes within the Native Lipid Environment

Lipid complexity of bacterial membranes and the dynamic interaction of lipophilic substrates with membrane‐embedded enzymes reflect a demand for a robust detection approach that unravels the local lipids and hydrophobic substrates/products either bound or within the milieu of membrane enzymes. In this study, we used styrene maleic acid lipid particle (SMALP) nanodiscs and electrospray ionization‐ion mobility spectrometry–mass spectrometry (ESI‐IMS) mass spectrometry to address the stability of lipid‐bound states of two bacterial β‐barrel enzymes. We overexpressed and purified different oligomeric states of two model β‐barrel enzymes with their co‐associated lipids (i.e. enzyme substrates/products) from the outer membrane of E.coli using various polymer formulations. We further examined the stability of the intact lipid‐protein nanodiscs in solution as well as in the gas phase. Our results, thus far, has demonstrated the higher efficacy of the native nanodiscs over conventional detergents in isolating lipid populations bound to the enzymes, also an improved thermal stability of the resulting β‐barrel complexes in solution. We have, interestingly, observed that some polymers are more compatible with the required conditions in mass spectrometry hence overcoming limitations (e.g. low pH which is known as destabilizing factor for the original SMALP nanodiscs) in the structural analysis of lipid‐bound states of membrane proteins in the gas phase. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .