Li Yanfeng, Dudek Jan, Guiard Bernard, Pfanner Nikolaus, Rehling Peter, Voos Wolfgang
Institut für Biochemie und Molekularbiologie, Universität Freiburg, D-79104 Freiburg, Germany.
J Biol Chem. 2004 Sep 3;279(36):38047-54. doi: 10.1074/jbc.M404319200. Epub 2004 Jun 24.
Transport of preproteins into the mitochondrial matrix requires the presequence translocase of the inner membrane (TIM23 complex) and the presequence translocase-associated motor (PAM). The motor consists of five essential subunits, the mitochondrial heat shock protein 70 (mtHsp70) and four cochaperones, the nucleotide exchange-factor Mge1, the translocase-associated fulcrum Tim44, the J-protein Pam18, and Pam16. Pam16 forms a complex with Pam18 and displays similarity to J-proteins but lacks the canonical tripeptide motif His-Pro-Asp (HPD). We report that Pam16 does not function as a typical J-domain protein but, rather, antagonizes the function of Pam18. Pam16 specifically inhibits the Pam18-mediated stimulation of the ATPase activity of mtHsp70. The inclusion of the HPD motif in Pam16 does not confer the ability to stimulate mtHsp70 activity. Pam16-HPD fully substitutes for wild-type Pam16 in vitro and in vivo but is not able to replace Pam18. Pam16 represents a new type of cochaperone that controls the stimulatory effect of the J-protein Pam18 and regulates the interaction of mtHsp70 with precursor proteins during import into mitochondria.
前体蛋白转运至线粒体基质需要内膜的前序列转位酶（TIM23复合物）和前序列转位酶相关分子马达（PAM）。该分子马达由五个必需亚基组成，即线粒体热休克蛋白70（mtHsp70）和四个辅助伴侣蛋白，核苷酸交换因子Mge1、转位酶相关支点蛋白Tim44、J结构域蛋白Pam18和Pam16。Pam16与Pam18形成复合物，与J结构域蛋白有相似性，但缺乏典型的His-Pro-Asp（HPD）三肽基序。我们报道Pam16并非作为典型的J结构域蛋白发挥作用，而是拮抗Pam18的功能。Pam16特异性抑制Pam18介导的mtHsp70 ATP酶活性的刺激作用。在Pam16中加入HPD基序并不能赋予其刺激mtHsp70活性的能力。Pam16-HPD在体外和体内完全可替代野生型Pam16，但无法取代Pam18。Pam16代表一种新型辅助伴侣蛋白，可控制J结构域蛋白Pam18的刺激作用，并在导入线粒体过程中调节mtHsp70与前体蛋白的相互作用。
