5UBC

The structure of the Arabidopsis thaliana Toc75 POTRA domains

Summary for 5UBC

• Entry DOI: 10.2210/pdb5ubc/pdb
• Descriptor: Protein TOC75-3, chloroplastic (1 entity in total)
• Functional Keywords: membrane protein, potra, chloroplast
• Biological source: Arabidopsis thaliana (Mouse-ear cress)
• Total number of polymer chains: 2
• Total formula weight: 72275.52

Authors

O'Neil, P.K.,Noinaj, N. (deposition date: 2016-12-20, release date: 2017-06-07, Last modification date: 2024-10-23)

Primary citation

O'Neil, P.K.,Richardson, L.G.L.,Paila, Y.D.,Piszczek, G.,Chakravarthy, S.,Noinaj, N.,Schnell, D.
The POTRA domains of Toc75 exhibit chaperone-like function to facilitate import into chloroplasts.
Proc. Natl. Acad. Sci. U.S.A., 114:E4868-E4876, 2017

PubMed Abstract: Protein trafficking across membranes is an essential function in cells; however, the exact mechanism for how this occurs is not well understood. In the endosymbionts, mitochondria and chloroplasts, the vast majority of proteins are synthesized in the cytoplasm as preproteins and then imported into the organelles via specialized machineries. In chloroplasts, protein import is accomplished by the TOC (translocon on the outer chloroplast membrane) and TIC (translocon on the inner chloroplast membrane) machineries in the outer and inner envelope membranes, respectively. TOC mediates initial recognition of preproteins at the outer membrane and includes a core membrane channel, Toc75, and two receptor proteins, Toc33/34 and Toc159, each containing GTPase domains that control preprotein binding and translocation. Toc75 is predicted to have a β-barrel fold consisting of an N-terminal intermembrane space (IMS) domain and a C-terminal 16-stranded β-barrel domain. Here we report the crystal structure of the N-terminal IMS domain of Toc75 from , revealing three tandem polypeptide transport-associated (POTRA) domains, with POTRA2 containing an additional elongated helix not observed previously in other POTRA domains. Functional studies show an interaction with the preprotein, preSSU, which is mediated through POTRA2-3. POTRA2-3 also was found to have chaperone-like activity in an insulin aggregation assay, which we propose facilitates preprotein import. Our data suggest a model in which the POTRA domains serve as a binding site for the preprotein as it emerges from the Toc75 channel and provide a chaperone-like activity to prevent misfolding or aggregation as the preprotein traverses the intermembrane space.

PubMed: 28559331
DOI: 10.1073/pnas.1621179114

Experimental method

X-RAY DIFFRACTION (2.862 Å)