Mass spectrometric identification of proteins released from mitochondria undergoing permeability transition

Mitochondrial membrane permeabilization is a rate-limiting step of cell dea th. This process is, at least in part, mediated by opening of the permeabil ity transition pore complex (PTPC) Several soluble proteins from the mitoch ondrial intermembrane space and matrix are involved in the activation of ca tabolic hydrolases including caspases and nucleases, We therefore investiga ted the composition of a mixture of proteins released from purified mitocho ndria upon PTPC opening,This mixture was subjected to a novel proteomics/ma ss spectrometric approach designed to identify a maximum of peptides, Pepti des from a total of 79 known proteins or genes were identified. In addition , 21 matches with expressed sequence tags (EST) were obtained, Among the kn own proteins, several may have indirect or direct pro-apoptotic properties. Thus endozepine, a ligand of the peripheral benzodiazepin receptor (whose occupation may facilitate mitochondrial membrane permeabilization), was fou nd among the released proteins. Several proteins involved in protein import were also released, namely the so-called X-linked deafness dystonia protei n (DDP) and the glucose regulated protein 75 (grb75), meaning that protein import may become irreversibly disrupted in mitochondria of apoptotic cells . In addition, a number of catabolic enzymes are detected: arginase 1 (whic h degrades arginine), sulfite oxidase (which degrades sulfur amino acids), and epoxide hydrolase, Although the functional impact of each of these prot eins on apoptosis remains elusive, the present data bank of mitochondrial p roteins released upon PTPC opening should help further elucidation of the d eath process.