Signaling Complexes Transferred by Outer Mitochondrial Membrane Mixing

The outer surface of the mitochondrion is home to a host of important signaling complexes. While it has been shown that fusion is an important regulator of mitochondrial health through the mixing of matrix contents and mtDNA complementation, little is known about the mixing of membranes, per se or of membrane associated proteins. Here we demonstrate by a PEG cell-fusion assay that two outer membrane associated signaling proteins--the A kinase anchoring protein, AKAP1 and the pro-apoptotic BCL-2 family member, BAD_are efficiently transferred during membrane mixing events. Using photoactivatible GFP fused to the targeting sequence of AKAP1 in combination with matrix targeted DsRed, we found that such events usually lead to the mixing of matrix contents within seconds, but in a fraction of cases the organelles separate without doing so, indicating a potentially distinct function and mechanism for the mixing of the outer membrane and associated proteins.