SEQUENTIAL ACTION OF 2 HSP70 COMPLEXES DURING PROTEIN IMPORT INTO MITOCHONDRIA

The mitochondrial chaperone mhsp70 mediates protein transport across t he inner membrane and protein folding in the matrix, These two reactio ns are effected by two different mhsp70 complexes, The ADP conformatio n of mhsp70 favors formation of a complex on the inner membrane; this 'import complex' contains mhsp70, its membrane anchor Tim44 and the nu cleotide exchange factor mGrpE. The ATP conformation of mhsp70 favors formation of a complex in the matrix; this 'folding complex' contains mhsp70, the mitochondrial DnaJ homolog Mdj1 and mGrpE. A precursor pro tein entering the matrix interacts first with the import complex and t hen with the folding complex, A chaperone can thus function as part of two different complexes within the same organelle.