Mapping of the protein import machinery in the mitochondrial outer membrane by crosslinking of translocation intermediates

Mitochondria contain a complex machinery for the import of
nuclear-encoded proteins. Receptor proteins exposed on the outer
membrane surface are required for the specific binding of precursor
proteins to mitochondria, either by binding of cytosolic signal
recognition factors or by direct recognition of the precursor
polypeptides. Subsequently, the precursors are inserted into the
outer membrane at the general insertion site GIP (general insertion
protein. Here we report the analysis of receptors and GIP by
crosslinking of translocation intermediates and by
coimmunoprecipitation. Surface-accumulated precursors were
cross-linked to the receptors MOM19 and MOM72, suggesting a direct
interaction of preproteins with surface receptors. We identified
three novel mitochondrial outer membrane proteins, MOM7, MOMS, and
MOM30 that, together with the previously identified MOM38, seem to
form the GIP site and are present in the mitochondrial receptor
complex.