Structure and Mechanistic Insights into Novel Iron-mediated Moonlighting Functions of Human J-protein Cochaperone, Dph4

Thakur, Anushikha and Chitoor, Balasubramanyam and Goswami, Arvind V and Pareek, Gautam and Atreya, Hanudatta S and D'Silva, Patrick (2012) Structure and Mechanistic Insights into Novel Iron-mediated Moonlighting Functions of Human J-protein Cochaperone, Dph4. In: Journal of Biological Chemistry, 287 (16). pp. 13194-13205.

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Abstract

J-proteins are obligate cochaperones of Hsp70s and stimulate their ATPase activity via the J-domain. Although the functions of J-proteins have been well understood in the context of Hsp70s, their additional co-evolved ``physiological functions'' are still elusive. We report here the solution structure and mechanism of novel iron-mediated functional roles of human Dph4, a type III J-protein playing a vital role in diphthamide biosynthesis and normal development. The NMR structure of Dph4 reveals two domains: a conserved J-domain and a CSL-domain connected via a flexible linker-helix. The linker-helix modulates the conformational flexibility between the two domains, regulating thereby the protein function. Dph4 exhibits a unique ability to bind iron in tetrahedral coordination geometry through cysteines of its CSL-domain. The oxidized Fe-Dph4 shows characteristic UV-visible and electron paramagnetic resonance spectral properties similar to rubredoxins. Iron-bound Dph4 (Fe-Dph4) also undergoes oligomerization, thus potentially functioning as a transient ``iron storage protein,'' thereby regulating the intracellular iron homeostasis. Remarkably, Fe-Dph4 exhibits vital redox and electron carrier activity, which is critical for important metabolic reactions, including diphthamide biosynthesis. Further, we observed that Fe-Dph4 is conformationally better poised to perform Hsp70-dependent functions, thus underlining the significance of iron binding in Dph4. Yeast Jjj3, a functional ortholog of human Dph4 also shows a similar iron-binding property, indicating the conserved nature of iron sequestration across species. Taken together, our findings provide invaluable evidence in favor of additional co-evolved specialized functions of J-proteins, previously not well appreciated.

Item Type:	Journal Article
Publication:	Journal of Biological Chemistry
Publisher:	The American Society for Biochemistry and Molecular Biology.
Additional Information:	Copyright of this article is belongs to The American Society for Biochemistry and Molecular Biology.
Department/Centre:	Division of Biological Sciences > Biochemistry Division of Chemical Sciences > NMR Research Centre (Formerly Sophisticated Instruments Facility) Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	22 Aug 2012 05:00
Last Modified:	22 Aug 2012 05:00
URI:	http://eprints.iisc.ac.in/id/eprint/44462

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