title: Cytosolic targeting factor AKR2A captures chloroplast outer membrane-localized client proteins at the ribosome during translation.
abstract: In eukaryotic cells, organellar proteome biogenesis is pivotal for cellular function. Chloroplasts contain a complex proteome, the biogenesis of which includes post-translational import of nuclear-encoded proteins. However, the mechanisms determining when and how nascent chloroplast-targeted proteins are sorted in the cytosol are unknown. Here, we establish the timing and mode of interaction between ankyrin repeat-containing protein 2 (AKR2A), the cytosolic targeting factor of chloroplast outer membrane (COM) proteins, and its interacting partners during translation at the single-molecule level. The targeting signal of a nascent AKR2A client protein residing in the ribosomal exit tunnel induces AKR2A binding to ribosomal RPL23A. Subsequently, RPL23A-bound AKR2A binds to the targeting signal when it becomes exposed from ribosomes. Failure of AKR2A binding to RPL23A in planta severely disrupts protein targeting to the COM; thus, AKR2A-mediated targeting of COM proteins is coupled to their translation, which in turn is crucial for biogenesis of the entire chloroplast proteome.
authors.affiliation: Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Dae Heon
authors.initials: DH
authors.lastname: Kim
authors.affiliation: Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Jae-Eun
authors.initials: JE
authors.lastname: Lee
authors.affiliation: Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Zheng-Yi
authors.initials: ZY
authors.lastname: Xu
authors.affiliation: Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Kyoung Rok
authors.initials: KR
authors.lastname: Geem
authors.affiliation: Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Yun
authors.initials: Y
authors.lastname: Kwon
authors.affiliation: Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Joon Won
authors.initials: JW
authors.lastname: Park
authors.affiliation: Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.|Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Inhwan
authors.initials: I
authors.lastname: Hwang
mesh_terms: D017360:Arabidopsis; D029681:Arabidopsis Proteins / Q000378:metabolism*; D060365:Chloroplast Proteins / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism; D003600:Cytosol; D007425:Intracellular Membranes / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D012269:Ribosomal Proteins / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism
chemical_list: C451699:AKR2 protein, Arabidopsis; D029681:Arabidopsis Proteins; D060365:Chloroplast Proteins; D018832:Molecular Chaperones; D012269:Ribosomal Proteins; C519026:ribosomal protein L23A, Arabidopsis