J Integr Plant Biol. ›› 2023, Vol. 65 ›› Issue (2): 408-416.DOI: 10.1111/jipb.13385

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Understanding protein translocation across chloroplast membranes: Translocons and motor proteins

Da Been Kim1†, Changhee Na1†, Inhwan Hwang2* and Dong Wook Lee1,3,4*   

  1. 1. Department of Integrative Food, Bioscience and Biotechnology, Chonnam National University, Gwangju 61186, Korea;
    2. Department of Life Sciences, Pohang University of Science and Technology, Pohang 37673, Korea;
    3. Department of Bioenergy Science and Technology, Chonnam National University, Gwangju 61186, Korea;
    4. Kumho Life Science Laboratory, Chonnam National University, Gwangju 61186, Korea
    These authors contributed equally to this work.
    *Correspondences: Inhwan Hwang (ihhwang@postech.ac.kr); Dong Wook Lee (ldw4844@jnu.ac.kr, Dr. Lee is fully responsible for the distribution of the material associated with this article)
  • Received:2022-08-29 Accepted:2022-10-11 Online:2022-10-12 Published:2023-02-01

Abstract: Subcellular organelles in eukaryotes are surrounded by lipid membranes. In an endomembrane system, vesicle trafficking is the primary mechanism for the delivery of organellar proteins to specific organelles. However, organellar proteins for chloroplasts, mitochondria, the nucleus, and peroxisomes that are translated in the cytosol are directly imported into their target organelles. Chloroplasts are a plant-specific organelle with outer and inner envelope membranes, a dual-membrane structure that is similar to mitochondria. Interior chloroplast proteins translated by cytosolic ribosomes are thus translocated through TOC and TIC complexes (translocons in the outer and inner envelope of chloroplasts, respectively), with stromal ATPase motor proteins playing a critical role in pulling pre-proteins through these import channels. Over the last three decades, the identity and function of TOC/TIC components and stromal motor proteins have been actively investigated, which has shed light on the action mechanisms at a molecular level. However, there remains some disagreement over the exact composition of TIC complexes and genuine stromal motor proteins. In this review, we discuss recent findings on the mechanisms by which proteins are translocated through TOC/TIC complexes and discuss future prospects for this field of research.

Key words: ATPase motor protein, chloroplast, molecular chaperone, protein translocation, TOC/TIC translocon

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