INTERACTIONS BETWEEN BRAIN MITOCHONDRIA AND CYTOSKELETON - EVIDENCE FOR SPECIALIZED OUTER-MEMBRANE DOMAINS INVOLVED IN THE ASSOCIATION OF CYTOSKELETON-ASSOCIATED PROTEINS TO MITOCHONDRIA IN-SITU AND IN-VITRO

The surface distribution of several proteins (porin, hexokinase, and t wo proteins associated with microtubules or actin filaments) on the ou ter membrane of brain mitochondria was analyzed by immunogold labellin g of purified mitochondria in vitro. The results suggest the existence of specialized domains for the distribution of porin in the outer mit ochondrial membrane. Similarities between the distribution of porin an d the distribution of microtubule-associated proteins bound in vitro t o mitochondria suggested that mitochondria and microtubules interact b y binding microtubule-associated proteins to porin-containing domains of the outer membrane. This hypothesis was supported by biochemical st udies on outer mitochondrial proteins involved in in vitro binding of cytoskeleton elements. In vitro interactions between mitochondria and microtubules or neurofilaments were analyzed by electron microscopy. T hese studies revealed cross-bridging between the outer membrane of mit ochondria and the two cytoskeleton elements. Cross-bridging was influe nced by ATP hydrolysis and by several proteins associated with the sur face of mitochondria or with microtubules. In addition, unidentified p roteins which were recognized by antibodies to all intermediate filame nts subunits were associated either with the mitochondrial surface or with microtubules. This data suggest the participation of additional c ytoplasmic proteins in the interactions between cytoskeleton elements and mitochondria. (C) 1994 Wiley-Liss, Inc.