Abstract
Blue native (BN) gel electrophoresis is a powerful method for protein separation. Combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS), it enables large scale identification of protein complexes and their subunits. Current BN-MS approaches, however, are limited in size resolution, comprehensiveness, and quantification. Here, we present a new methodology combining defined sub-millimeter slicing of BN gels by a cryo-microtome with high performance LC-MS/MS and label-free quantification of protein amounts. Application of this cryo-slicing BN-MS approach to mitochondria from rat brain demonstrated a high degree of comprehensiveness, accuracy, and size resolution. The technique provided abundance-mass profiles for 774 mitochondrial proteins, including all canonical subunits of the oxidative respiratory chain assembled into 13 distinct (super-)complexes. Moreover, the data revealed COX7R as a constitutive subunit of distinct super-complexes and identified novel assemblies of voltage-dependent anion channels/porins and TOM proteins. Together, cryo-slicing BN-MS enables quantitative profiling of complexomes with resolution close to the limits of native gel electrophoresis.