Disease relevance of MDJ1

• We have purified a mature form of Ssc1p from yeast mitochondria and those of Mdj1p and Yge1p from Escherichia coli overexpresser cells [1].
• This toxicity was specifically relieved by mutations which affected the putative zinc binding region of Mdj1p [2].

High impact information on MDJ1

• Disruption of the MDJ1 gene resulted in a petite phenotype, loss of mitochondrial DNA, and inviability at 37 degrees C. Import of precursor proteins was not affected by a lack of Mdj1p, but folding of newly imported proteins was markedly impaired [3].
• Mdj1p, a novel member of the DnaJ family, is a heat shock protein that is associated with the inner membrane of mitochondria of Saccharomyces cerevisiae [3].
• Mdj1p, a novel chaperone of the DnaJ family, is involved in mitochondrial biogenesis and protein folding [3].
• The efficiency of refolding of a tester protein, dihydrofolate reductase, was significantly reduced in mitochondria lacking Mdj1p after incubation at elevated temperature [3].
• On the other hand, J domains from two other non-ER DnaJs, Sis1p and Mdj1p, do not function when swapped into Sec63p [4].

Biological context of MDJ1

• Mitochondrial genomes were rapidly lost in a temperature-sensitive mdj1 mutant under nonpermissive conditions [5].
• On the other hand, the fast refolding process is most enhanced when luciferase is incubated with Ssc1p alone at 42 degreesC, and it requires neither the assistance of Mdj1p and Yge1p nor ATP hydrolysis [1].

Anatomical context of MDJ1

• The PbMDJ1 gene belongs to a conserved MDJ1/LON locus in thermodimorphic pathogenic fungi and encodes a heat shock protein that localizes to both the mitochondria and cell wall of Paracoccidioides brasiliensis [6].
• Mdj1p and mt-Hsp70 were found in a complex with nascent polypeptide chains on mitochondrial ribosomes [7].
• In the present study, we have demonstrated the presence of Mdj1, a mitochondrial DnaJ member, not only in the mitochondria, where it is apparently sorted, but also in the cell wall of Paracoccidioides brasiliensis, a thermodimorphic pathogenic fungus [6].

Associations of MDJ1 with chemical compounds

• Overexpression of a truncated version of Mdj1p, containing the J- and Gly/Phe-rich domains, partially substituted for DnaJ function at high temperature [2].

Regulatory relationships of MDJ1

• Here we show that the expression of Saccharomyces cerevisiae MDJ1 encoding a mitochondrial DnaJ homolog is regulated by HSF via a novel non-consensus HSE (ncHSE(MDJ1)), which consists of three separated pentameric nGAAn motifs, nTTCn-(11 bp)-nGAAn-(5 bp)-nGAAn [8].
• The mitochondrially encoded var1 protein showed enhanced aggregation after synthesis in mdj1 mutant mitochondria [7].

Other interactions of MDJ1

• Using the mRNA differential display technique, six genes were found to be up-regulated: ASN2, MDJ1, YLR194c, YNL208w, YER175, and YGL121c [9].
• Studies on the chaperone activity of Hsp78 show that its cooperation with the mitochondrial Hsp70 system, consisting of Ssc1p, Mdj1p and Mge1p, is needed for the efficient reactivation of substrate proteins [10].
• In the mitochondria of Saccharomyces cerevisiae the three corresponding members are designated as Ssc1p, Mdj1p, and Mge1p, respectively [11].
• However, even under these conditions, no interaction of Ssq1 with the two other mitochondrial Hsp70-cochaperones, Tim44 and Mdj1, was observed [12].
• The mitochondrial DnaJ homolog Jac1 is crucial for this process, whereas Mdj1 function is dispensable [13].

References