Modulation of chaperone activities of Hsp70 and Hsp70-2 by a mammalian DnaJ/Hsp40 homolog, DjA4.
Type I DnaJs comprise one type of Hsp70 cochaperones. Previously, we showed that two type I DnaJ cochaperones, DjA1 (HSDJ/Hdj-2/Rdj-1/dj2) and DjA2 (cpr3/DNAJ3/Rdj-2/dj3), are important for mitochondrial protein import and luciferase refolding. Another type I DnaJ homolog, DjA4 (mmDjA4/dj4), is highly expressed in heart and testis, and the coexpression of Hsp70 and DjA4 protects against heat stress-induced cell death. Here, we have studied the chaperone functions of DjA4 by assaying the refolding of chemically or thermally denatured luciferase, suppression of luciferase aggregation, and the ATPase of Hsp70s, and compared these activities with those of DjA2. DjA4 stimulates the hydrolysis of ATP by Hsp70. DjA2, but not DjA4, together with Hsp70 caused denatured luciferase to refold efficiently. Together with Hsp70, both DjA2 and DjA4 are efficient in suppressing luciferase aggregation. bag-1 further stimulates ATP hydrolysis and protein refolding by Hsp70 plus DjA2 but not by Hsp70 plus DjA4. Hsp70-2, a testis-specific Hsp70 family member, behaves very similarly to Hsp70 in all these assays. Thus, Hsp70 and Hsp70-2 have similar activities in vitro, and DjA2 and DjA4 can function as partner cochaperones of Hsp70 and Hsp70-2. However, DjA4 is not functionally equivalent in modulating Hsp70s.
Hafizur
Rahman Md
RM
Department of Molecular Genetics, Graduate School of Medical Sciences, Kumamoto University, Honjo 1-1-1, Kumamoto 860-8556.
Yano
Masato
M
Gotoh
Tomomi
T
Mori
Masataka
M
Terada
Kazutoyo
K
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002470:Cell Survival; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism*; D006358:Hot Temperature; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism*; D011489:Protein Denaturation; D017510:Protein Folding; D013737:Testis / Q000378:metabolism; D013997:Time Factors
C494647:DNAJB1 protein, human; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C091879:HSPA2 protein, human; D006360:Heat-Shock Proteins; C490434:Hspa2 protein, mouse; D018832:Molecular Chaperones; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases