Structural highlights
Function
TOC75_PEA Mediates the insertion of proteins targeted to the outer membrane of chloroplasts. Required for the import of protein precursors into chloroplasts. Forms the voltage-dependent preprotein translocation channels (hydrophilic beta barrel) of the TOC complex in the chloroplastic outer membrane. The narrowest inner diameter of this channel is approximately 14 Angstroms.[1] [2] [3] [4] [5]
Publication Abstract from PubMed
Roughly 95% of the proteins that make up the chloroplast must be imported from the cytoplasm. The machinery responsible for the translocation of these cargo proteins is called the translocon at the outer membrane of chloroplast (TOC). The TOC core consists of three proteins, Toc34, Toc75, and Toc159; no high-resolution structure has been solved of fully assembled TOC from plants. Efforts toward determining the structure of the TOC have been hindered almost entirely by difficulties in producing sufficient yields for structural studies. In this study, we introduce an innovative method that utilizes synthetic antigen binding fragments (sABs) to isolate TOC directly from wild-type plant biomass including A. thaliana and P. sativum. Binding between the sABs and the POTRA domains was characterized by size-exclusion chromatography coupled with small-angle X-ray scattering (SEC-SAXS), X-ray crystallography, and isothermal titration calorimetry. We also demonstrate the isolation of the TOC from P. sativum, laying the framework for large-scale isolation and purification of TOC for functional and structural studies.
Characterization of synthetic antigen binding fragments targeting Toc75 for the isolation of TOC in A. thaliana and P. sativum.,Srinivasan K, Erramilli SK, Chakravarthy S, Gonzalez A, Kossiakoff A, Noinaj N Structure. 2023 May 4;31(5):595-606.e5. doi: 10.1016/j.str.2023.03.002. Epub 2023 , Mar 27. PMID:36977410[6]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Tu SL, Chen LJ, Smith MD, Su YS, Schnell DJ, Li HM. Import pathways of chloroplast interior proteins and the outer-membrane protein OEP14 converge at Toc75. Plant Cell. 2004 Aug;16(8):2078-88. PMID:15258267 doi:10.1105/tpc.104.023952
- ↑ Tranel PJ, Froehlich J, Goyal A, Keegstra K. A component of the chloroplastic protein import apparatus is targeted to the outer envelope membrane via a novel pathway. EMBO J. 1995 Jun 1;14(11):2436-46. PMID:7781598 doi:10.1002/j.1460-2075.1995.tb07241.x
- ↑ Schnell DJ, Kessler F, Blobel G. Isolation of components of the chloroplast protein import machinery. Science. 1994 Nov 11;266(5187):1007-12. PMID:7973649 doi:10.1126/science.7973649
- ↑ Nielsen E, Akita M, Davila-Aponte J, Keegstra K. Stable association of chloroplastic precursors with protein translocation complexes that contain proteins from both envelope membranes and a stromal Hsp100 molecular chaperone. EMBO J. 1997 Mar 3;16(5):935-46. PMID:9118955 doi:10.1093/emboj/16.5.935
- ↑ Hinnah SC, Hill K, Wagner R, Schlicher T, Soll J. Reconstitution of a chloroplast protein import channel. EMBO J. 1997 Dec 15;16(24):7351-60. PMID:9405364 doi:10.1093/emboj/16.24.7351
- ↑ Srinivasan K, Erramilli SK, Chakravarthy S, Gonzalez A, Kossiakoff A, Noinaj N. Characterization of synthetic antigen binding fragments targeting Toc75 for the isolation of TOC in A. thaliana and P. sativum. Structure. 2023 May 4;31(5):595-606.e5. PMID:36977410 doi:10.1016/j.str.2023.03.002
