Proceedings of the Nutrition Society

Symposium 3: Mechanisms involved in exercise-induced mitochondrila biogenesis in skeletal muscle

Mitochondrial assembly: protein import

David A. Hooda1 c1 and Anna-Maria Josepha1

a1 School of Kinesiology and Health Science and Department of Biology, York University, Toronto, Ontario M3J 1P3, Canada


The protein import process of mitochondria is vital for the assembly of the hundreds of nuclear-derived proteins into an expanding organelle reticulum. Most of our knowledge of this complex multisubunit network comes from studies of yeast and fungal systems, with little information known about the protein import process in mammalian cells, particularly skeletal muscle. However, growing evidence indicates that the protein import machinery can respond to changes in the energy status of the cell. In particular, contractile activity, a powerful inducer of mitochondrial biogenesis, has been shown to alter the stoichiometry of the protein import apparatus via changes in several protein import machinery components. These adaptations include the induction of cytosolic molecular chaperones that transport precursors to the matrix, the up-regulation of outer membrane import receptors, and the increase in matrix chaperonins that facilitate the import and proper folding of the protein for subsequent compartmentation in the matrix or inner membrane. The physiological importance of these changes is an increased capacity for import into the organelle at any given precursor concentration. Defects in the protein import machinery components have been associated with mitochondrial disorders. Thus, contractile activity may serve as a possible mechanism for up-regulation of mitochondrial protein import and compensation for mitochondrial phenotype alterations observed in diseased muscle.


c1 *Corresponding author: Dr David A. Hood Fax: +1 416 736 5698, Email: