title: An ankyrin repeat domain of AKR2 drives chloroplast targeting through coincident binding of two chloroplast lipids.
abstract: In organellogenesis of the chloroplast from endosymbiotic cyanobacteria, the establishment of protein-targeting mechanisms to the chloroplast should have been pivotal. However, it is still mysterious how these mechanisms were established and how they work in plant cells. Here we show that AKR2A, the cytosolic targeting factor for chloroplast outer membrane (COM) proteins, evolved from the ankyrin repeat domain (ARD) of the host cell by stepwise extensions of its N-terminal domain and that two lipids, monogalactosyldiacylglycerol (MGDG) and phosphatidylglycerol (PG), of the endosymbiont were selected to function as the AKR2A receptor. Structural analysis, molecular modeling, and mutational analysis of the ARD identified two adjacent sites for coincidental and synergistic binding of MGDG and PG. Based on these findings, we propose that the targeting mechanism of COM proteins was established using components from both the endosymbiont and host cell through a modification of the protein-protein-interacting ARD into a lipid binding domain.
authors.affiliation: Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Dae Heon
authors.initials: DH
authors.lastname: Kim
authors.affiliation: Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Mi-Jeong
authors.initials: MJ
authors.lastname: Park
authors.affiliation: Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Gwang Hyeon
authors.initials: GH
authors.lastname: Gwon
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Columbia University, New York, NY 11032, USA.
authors.forename: Antonina
authors.initials: A
authors.lastname: Silkov
authors.affiliation: Division of Molecular and 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 Biological Sciences, Sungkyunkwan University, Suwon 440-746, Korea.
authors.forename: Eun Chan
authors.initials: EC
authors.lastname: Yang
authors.affiliation: Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA.
authors.forename: Seohyeon
authors.initials: S
authors.lastname: Song
authors.affiliation: Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Kyungyoung
authors.initials: K
authors.lastname: Song
authors.affiliation: Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Younghyun
authors.initials: Y
authors.lastname: Kim
authors.affiliation: Department of Biological Sciences, Sungkyunkwan University, Suwon 440-746, Korea.
authors.forename: Hwan Su
authors.initials: HS
authors.lastname: Yoon
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Columbia University, New York, NY 11032, USA.
authors.forename: Barry
authors.initials: B
authors.lastname: Honig
authors.affiliation: Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 790-784, Korea; Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA. Electronic address: wcho@uic.edu.
authors.forename: Wonhwa
authors.initials: W
authors.lastname: Cho
authors.affiliation: Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea. Electronic address: yunje@postech.ac.kr.
authors.forename: Yunje
authors.initials: Y
authors.lastname: Cho
authors.affiliation: Division of Molecular and 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. Electronic address: ihhwang@postech.ac.kr.
authors.forename: Inhwan
authors.initials: I
authors.lastname: Hwang
mesh_terms: D000595:Amino Acid Sequence; D017089:Ankyrin Repeat; D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D001665:Binding Sites; D002736:Chloroplasts / Q000378:metabolism*; D000458:Cyanobacteria / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D038983:Galactolipids / Q000737:chemistry; D008055:Lipids / Q000737:chemistry*; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry* / Q000502:physiology; D008969:Molecular Sequence Data; D010715:Phosphatidylglycerols / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013559:Symbiosis
chemical_list: C451699:AKR2 protein, Arabidopsis; D029681:Arabidopsis Proteins; D038983:Galactolipids; D008055:Lipids; D018832:Molecular Chaperones; D010715:Phosphatidylglycerols; C009909:monogalactosyldiacylglycerol