MDJ1

Mdj1 is a mitochondrial Hsp40-type co-chaperone protein in the budding yeast Saccharomyces cerevisiae. The name stands for mitochondrial DnaJ homolog 1. Mdj1 is encoded by the MDJ1 gene and is targeted to the mitochondrial matrix by an N-terminal targeting sequence. It functions as a co-chaperone for the mitochondrial Hsp70 chaperone Ssc1, stimulating ATP hydrolysis and thereby promoting productive binding and release of mitochondrial precursor polypeptides during import and folding.

Mdj1 operates as part of the mitochondrial protein import machinery, aiding translocation of proteins across the inner membrane and facilitating correct folding after import. It also contributes to the oxidative folding and maturation of certain matrix proteins and helps prevent aggregation under stress. Genetic studies indicate that loss of MDJ1 impairs mitochondrial import and respiration, with slower growth on nonfermentable carbon sources and increased sensitivity to heat and chemical stress; however, Mdj1 is not strictly essential for viability under rich conditions, suggesting redundancy with other chaperone systems.

Mdj1 has orthologs in other eukaryotes, reflecting conservation of the DnaJ/Hsp40 family in mitochondria. Research on Mdj1 informs understanding of mitochondrial biogenesis, protein quality control, and the regulation of the mitochondrial chaperone network.