Chapter 1 Mitochondrial Protein Import: Specific Recognition and Membrane Insertion of Precursor Proteins

Abstract

Publisher Summary The question of how proteins are directed to their specific target membrane and how they are translocated into and across organellar membranes pose a central theme of modern cell biology. Most of the organellar proteins are synthesized as precursor proteins on cytosolic polysomes and thus have to be transported to their functional destination. The cytosolic precursor proteins carry specific targeting sequences that are assumed to bind to complementary structures (“receptors”) on the surface of organelles. Mitochondrial proteins import that the translocation of precursor proteins across membranes is not mechanistically coupled to the synthesis of the protein on ribosomes, both in vivu and in vitro. Presequences contain signal information for translocation into mitochondria. With some precursor proteins, targeting sequences were also found in nonamino-terminal (carboxyl-terminal) regions of the polypeptide. The precursor proteins are recognized by specific receptors on the mitochondrial surface and are then inserted into the outer membrane. Functional characterization of initial steps of mitochondrial protein import provided the tools for the identification of two mitochondrial outer membrane proteins––MOM 19 and MOM72––as specific receptors for precursor proteins.