Abstract:

Mitochondrial biogenesis requires the import of proteins coded for in the nucleus, translated in the cytosol, and translocated to the various mitochondrial compartments, including the IMS and the matrix, as well as the outer and inner membranes. Proteins imported via the TIM22 import pathway cross the outer membrane at the TOM complex and are inserted into the inner membrane by the TIM22 complex. The small, soluble TIM8/13 and TIM9/10 complexes act as chaperones to facilitate the crossing of the aqueous IMS by the incoming hydrophobic inner membrane proteins.

A redox pathway (Mia40p and Erv1p) mediates the import of the small Tim proteins necessary to form the TIM8/13 and TIM9/10 complexes. These monomer small Tim proteins (Tims 8, 9, 10, 12) possess a twin CX3C motif and contain disulfide linkages essential for function. Through a "folding trap" mechanism, the small Tims are imported and trapped in the IMS through the formation of an intramolecular disulfide bond. The small Tims are oxidized by the action of Mia40p, which is itself oxidized by the sulfhydryl oxidase Erv1p. Erv1p is capable of synthesizing disulfide bonds de novo , using O2 , cyt c , or Ccp1 as a terminal electron acceptor. Once the small Tims are imported and oxidized, it is the action of Hot13p, localized in the IMS, to form the oxidized monomers into functional complexes.

Mitochondrial import has been studied primarily in the budding yeast Saccharomyces cerevisiae , which is an excellent model system for biochemical and genetic studies. However, this model system excludes the possibility of examining the effect of protein import defects on the development of an organism. To this end, I examined mitochondrial import using the organism Caenorhabditis elegans , thus establishing a new model system for the study of development as related to mitochondrial import. This, along with studies I have completed in yeast, have allowed the characterization of the small Tim proteins, the elucidation of the role of redox chemistry in protein import into mitochondria, and the understanding of import defects on development.