PDBsum entry 5ubc

Membrane protein

PDB id: 5ubc

Contents

Protein chains

300 a.a.

PDB id:

5ubc

Name:

Membrane protein

Title:

The structure of the arabidopsis thaliana toc75 potra domains

Structure:

Protein toc75-3, chloroplastic. Chain: a, b. Synonym: 75 kda translocon at the outer-envelope-membrane of chloroplasts 3,attoc75-iii. Engineered: yes

Source:

Arabidopsis thaliana. Mouse-ear cress. Organism_taxid: 3702. Gene: toc75-3, toc75, at3g46740, t6h20.230. Expressed in: escherichia coli. Expression_system_taxid: 469008.

Resolution:

2.86Å R-factor: 0.230 R-free: 0.280

Authors:

P.K.O'Neil,N.Noinaj

Key ref:

P.K.O'Neil et al. (2017). The POTRA domains of Toc75 exhibit chaperone-like function to facilitate import into chloroplasts. Proc Natl Acad Sci U S A, 114, E4868. PubMed id: 28559331

Date:

20-Dec-16 Release date: 07-Jun-17

Protein chains

Q9STE8  (TC753_ARATH) -  Protein TOC75-3, chloroplastic from Arabidopsis thaliana

Seq: 818 a.a.

Struc: 300 a.a.

Proc Natl Acad Sci U S A 114:E4868 (2017)

PubMed id: 28559331

The POTRA domains of Toc75 exhibit chaperone-like function to facilitate import into chloroplasts.

P.K.O'Neil, L.G.L.Richardson, Y.D.Paila, G.Piszczek, S.Chakravarthy, N.Noinaj, D.Schnell.

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 fromArabidopsis thaliana, 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.