AtTPR7 is a chaperone docking protein of the Sec translocon in Arabidopsis

Abstract

Chaperone assisted sorting of post-translationally imported proteins is a general mechanism among all eukaryotic organisms. Interaction of some preproteins with the organellar membranes is mediated by chaperones, which are recognized by membrane bound tetratricopeptide repeat (TPR) domain containing proteins. We have characterized AtTPR7 as an endoplasmic reticulum (ER) protein in plants and propose a potential function for AtTPR7 in post-translational protein import. Our data demonstrate that AtTPR7 interacts with the heat shock proteins HSP90 and HSP70 via a cytosolic exposed TPR domain. We further show by in vitro and in vivo experiments that AtTPR7 is associated with the Arabidopsis Sec63 homologue, AtERdj2. Interestingly, AtTPR7 can functionally complement a Δsec71 yeast mutant which is impaired in post-translational protein transport. These data strongly suggest that AtTPR7 not only has a role in chaperone binding but also in post-translational protein import into the ER, pointing to a general mechanism of chaperone mediated post-translational sorting between the ER, mitochondria and chloroplasts in plant cells.