INTERACTION OF A DIMERIC MITOCHONDRIAL PRECURSOR WITH PHOSPHOLIPID-VESICLES - DIRECT ASSOCIATION OF EACH SUBUNIT WITH THE MEMBRANE IS REQUIRED FOR LOSS OF FUNCTIONALITY

Binding of the precursor to mitochondrial aspartate aminotransferase t o anionic phospholipid vesicles results in the loss of catalytic activ ity, apparently due to the inability of the bound protein to undergo t he conformational transitions required for catalysis [A. Berezov, A. I riarte, and M. Martinez-Carrion (1994) J. Biol. Chem. 269, 22222-22229 ]. Light scattering and electron microscopy analysis indicate that pre sequence-dependent binding of the precursor leads to extensive vesicle aggregation brought about by their cross-linking through interaction of each of the two presequences of this dimeric protein with separate vesicles. To evaluate the possible contribution of this aggregation to the properties of the bound protein, we analyzed the membrane interac tion of a hybrid dimer containing a single presequence peptide. This d imer still binds to vesicles but does not cause aggregation. The prope rties of the bound hybrid are intermediate between those of the free a nd bound home-precursor dimer with only the presequence-carrying subun it showing alterations in its structural and functional properties. Th ese results indicate that the conformational perturbation of the matur e moiety of lipid-bound precursor is caused by the direct interaction of each subunit with the membrane through its own N-terminal presequen ce peptide. (C) 1996 Academic Press, Inc.