| Popis: |
Publisher Summary This chapter presents the general pathways for protein import into sub-mitochondrial compartments. The consensus pathways for protein sorting into the different mitochondrial compartments are presented. Nuclear encoded mitochondrial proteins are synthesized on cytoplasmic ribosomes as precursors, which usually contain N-terminal targeting (signal) sequences. These signal peptides are positively charged and have the potential to form amphipathic a-helices. Some precursor proteins, however, lack such cleavable pre-sequences, such as those destined for the mitochondrial outer membrane (OM). Specific interaction of most precursor proteins with the OM is mediated by protease-sensitive surface receptors. Neurospora crassa MOM 19 acts as the receptor for the majority of proteins analyzed so far, whereas the participation of N.crassa MOM72 has been demonstrated only in connection with the import of the ADP/ATP carrier. Translocation through or insertion into the OM is catalyzed by a number of proteins which are associated in a complex in the OM. This complex has been identified by co-immunoprecipitation with the surface receptors MOM19 or MOM72, which are part of the complex. One of its components, N.crassa MOM38, is part of a translocation site in which the precursor proteins are already deeply inserted in the OM and thus are resistant to externally added protease. The yeast counterpart of MOM38, ISP42, is essential for cell growth. |
