研究発表を行った学会；第７６回日本生化学会年会
２００４年１０月１５日〜１０月１８日（東京）
タイトル；Modulation of Chaperone Activities of Hsp70 and Hsp70-2 by a Mammalian DnaJ/Hsp40 Homolog, DjA4
発表者；Rahman Md. Hafizur,　氏
　　　（熊本大学　大学院医学薬学研究部　分子遺伝分野）
Abstract；
Type I DnaJs are one of the cochaperones of Hsp70s. We showed that two of 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 coexpression of Hsp70 and DjA4 protected heat stress cell death.
Here, we studied the chaperone functions of DjA4 by assaying refolding of chemically or thermally denatured luciferase, suppression of luciferase aggregation, and ATPase of Hsp70s, and compared these activities with those of DjA2. DjA4 stimulated the hydrolysis of ATP by Hsp70. DjA2, but not DjA4, together with Hsp70 refolded the denatured luciferase efficiently. Together with Hsp70, both DjA2 and DjA4 were efficient in suppressing luciferase aggregation. bag-1 further stimulated ATP hydrolysis and protein refolding by Hsp70 plus DjA2 but not by Hsp70 plus DjA4. Hsp70-2, a testis-specific Hsp70 family member, behaved very similarly with 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.