Identification and characterization of a mammalian mitochondrial ATP-binding cassette membrane protein

Membrane proteins of the AT-binding cassette (ABC) superfamily are involved in the transport of diverse substrates across organellar and plasma membra nes of the mammalian cell. Most human ABC proteins identified to date are a ssociated with genetically linked diseases or clinically relevant phenotype s. We describe a new human half-molecule ABC protein, designated M-ABC1, th at contains a predicted single membrane and ATP-binding cassette domain. M- ABC1 is localized to membranes of the mitochondria and its transcript is ex pressed in all tissues. The N-terminal region of the M-ABC1 protein was sho wn to function independently as a mitochondrial signal sequence by its abil ity to target the green fluorescent protein to the mitochondria. The monome ric 60 kDa M-ABC1 protein was chemically crosslinked in vivo into a major p rotein species of 120-130 kDa, thereby confirming that M-ABC1 exists within a higher ordered ABC protein complex. A dominant negative repression appro ach using M-ABC1 protein with site-directed mutations in its Walker A motif revealed that the mutant protein was rapidly degraded and indicated that t he intact Walker A motif of M-ABC1 was required for its stability. The iden tification of M-ABC1 extends the known distribution of members of the ABC p rotein family into the mammalian mitochondrion. (C) 1999 Academic Press.