Structural and functional insights of HSP90C, the chloroplastic HSP90 family member.

authors

• La Rocca Romain
• Chenuel Thomas
• Bergonzi Celine
• Meyer Philippe

keywords

• Molecular chaperone
• HSP90
• HSP90C

abstract

The Hsp90 family has been largely studied through the last 30 years, so that now its molecular mechanisms and pathological implications are well known in various species. However, a subset of Hsp90 proteins, namely the stromal Hsp90 proteins, are less described. More specifically, Hsp90C, the main Hsp90 of the chloroplast, is very poorly known despite its crucial role in protein import, which is essential for photosynthesis. Here we provide functional and structural insights of Hsp90C by means of biophysical approaches. First, we show that the N-terminal cap and the C-terminal tail of Hsp90C regulates its ATPase activity. Further investigation with SEC experiments showed that the N-terminal cap is also involved in the oligomerization of Hsp90C. Second, using in vitro luciferase refolding assays with the full bacterial refolding machinery, we show that Hsp90C is able to stimulate the renaturation of luciferase induced by DnaK. Finally, we obtained the first crystallographic structure of the middle and the C-terminal domains of the Hsp90C dimer. Noticeably, the structure reveals a larger lumen in comparison to the other Hsp90 members, through which Hsp90C may interact with a reduced subset of client proteins in the chloroplast. Our results show that Hsp90C is able to stimulate the refolding of HSP70 provided client regulated by its N-terminal and C-terminal extremities and provides a first structure of the Hsp90C dimer.

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