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Both metaxin and Tom20 together with two mitochondria-specific motifs support mitochondrial targeting of dual-targeting AtSufE1

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Journal of Integrative Plant Biology 2022年第8期64卷 1596-1613页

作者： Seungjin Woo Byeongho Moon inhwan hwang Department of Life Sciences Pohang University of Science and TechnologyPohang 790‐784Korea

Plant cells have two endosymbiotic organelles,chloroplasts,and mitochondria.These organelles perform specific functions that depend on organelle-specific proteins.The majority of chloroplast and mitochondrial proteins are specifically imported by the transit peptide and presequence,respectively.However,a significant number of proteins are also dually targeted to these two organelles.Currently,it is not fully understood how proteins are dually targeted to both chloroplasts and mitochondria.In this study,the mechanism underlying mitochondrial targeting of dual targeting At Suf E1 in Arabidopsis was elucidated.The N-terminal fragment containing 80 residues of AtSufE1(AtSufE1N80)was sufficient to confer dual targeting of reporter protein,At SufE1N80:GFP,in protoplasts.Two sequence motifs,two arginine residues at 15and 21positions,and amino acid(aa)sequence motif AKTLLLRPLK from the 31to 40aa position,were responsible for targeting to mitochondria a portion of reporter proteins amid the chloroplast targeting.The sequence motif PSEVPFRRT from the 41 stto 50 thaa position constitutes a common motif for targeting to both chloroplasts and mitochondria.For mitochondrial import of At Suf E1:N80,Metaxin played a critical role.In addition,Bi FC and protein pull-down experiments showed that At Suf E1N80 specifically interacts with import receptors,Metaxin and Tom20.The interaction of At Suf E1N80 with Metaxin was required for the interaction with Tom20.Based on these results,we propose that mitochondrial targeting of dual-targeting At Suf E1 is mediated by both mitochondria-specific and common sequence motifs in the signal sequence through the interaction with import receptors,Metaxin and Tom20,in a successive manner.

关键词： AtSufE1 chloroplasts common motif dual targeting metaxin mitochondria mitochondria-specific motif Tom20

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Translation rate underpins specific targeting of N-terminal transmembrane proteins to mitochondria

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Journal of Integrative Plant Biology 2023年第6期65卷 1505-1520页

作者： Junho Lee Byeongho Moon Dong Wook Lee inhwan hwang Department of Life Science Pohang University of Science and TechnologyPohang 790-784South Korea Department of Integrative Food Bioscience and BiotechnologyChonnam National UniversityGwangju 61186South Korea Department Bioenergy Science and Technology Chonnam National UniversityGwangju 61186South Korea

Protein biogenesis is a complex process,and complexity is greatly increased in eukaryotic cells through specific targeting of proteins to different organelles.To direct targeting,organellar proteins carry an organelle-specific targeting signal for recognition by organelle-specific import machinery.However,the situation is confusing for transmembrane domain(TMD)-containing signalanchored(SA)proteins of various organelles because TMDs function as an endoplasmic reticulum(ER)targeting signal.Although ER targeting of SA proteins is well understood,how they are targeted to mitochondria and chloroplasts remains elusive.Here,we investigated how the targeting specificity of SA proteins is determined for specific targeting to mitochondria and chloroplasts.Mitochondrial targeting requires multiple motifs around and within TMDs:a basic residue and an arginine-rich region flanking the N-and C-termini of TMDs,respectively,and an aromatic residue in the C-terminal side of the TMD that specify mitochondrial targeting in an additive manner.These motifs play a role in slowing down the elongation speed during translation,thereby ensuring mitochondrial targeting in a cotranslational manner.By contrast,the absence of any of these motifs individually or together causes at varying degrees chloroplast targeting that occurs in a post-translational manner.

关键词： arginine-rich region ER targeting mitochondria targeting organelle targeting TMD translational slowdown transmembrane domain

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Understanding protein translocation across chloroplast membranes:Translocons and motor proteins

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Journal of Integrative Plant Biology 2023年第2期65卷 408-416页

作者： Da Been Kim Changhee Na inhwan hwang Dong Wook Lee Department of Integrative Food Bioscience and BiotechnologyChonnam National UniversityGwangju 61186Korea Department of Life Sciences Pohang University of Science and TechnologyPohang 37673Korea Department of Bioenergy Science and Technology Chonnam National UniversityGwangju 61186Korea Kumho Life Science Laboratory Chonnam National UniversityGwangju 61186Korea

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.

关键词： ATPase motor protein chloroplast molecular chaperone protein translocation TOC/TIC translocon

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Liquid-Liquid Phase Transition as a New Means of Protein Targeting in Chloroplasts

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Molecular Plant 2020年第5期13卷 679-681页

作者： Dong Wook Lee inhwan hwang Department of Integrative Food Bioscience and BiotechnologyChonnam National UniversityGwangju 61186Korea Department of Bioenergy Science and Technology Chonnam National UniversityGwangju 61186Korea Division of Integrative Biosciences and Biotechnology Pohang University of Science and TechnologyPohang 37673Korea Department of Life Sciences Pohang University of Science and TechnologyPohang 37673t Korea

The chloroplast is a unique organelle in that it possesses an intra-organellar membrane-enclosed structure called thylakoid,which is central to photosynthesis.Thus,the timely expression and correct localization of thylakoid proteins are of utmost importance to plant growth and development(Lee et al.,2017;New et al.,2018).Biogenesis of thylakoid proteins is highly complex;they are encoded by two different genomes,nuclear and chloroplast genomes,and translated in the cytosol and chloroplasts,respectively.Nuclear-encoded thylakoid proteins are first imported into the stroma of chloroplasts before they are targeted to thylakoids.In the stroma,multiple sorting mechanisms exist to ensure import or insertion of thylakoid luminal or membrane proteins,respectively(Lee et al.,2017).Approximately 50%of thylakoid luminal proteins are imported through the cpTAT(chloroplast twin-arginine translocation)pathway,which is also present in bacteria and plant mitochondria(Cline,2015;Schafer et al.f 2020).

关键词： al. Transition insertion

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The A/ENTH Domain-Containing Protein AtECA4 Is an Adaptor Protein Involved in Cargo Recycling from the trans-Golgi Network/Early Endosome to the Plasma Membrane

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Molecular Plant 2018年第4期11卷 568-583页

作者： Hong Hanh Nguyen Myoung Hui Lee Kyungyoung Song Gyeongik Ahn Jihyeong Lee inhwan hwang Division of Integrative Biosciences and Biotechnology Pohang University of Science and Technology Pohang 790-784 Korea Department of Life Sciences Pohang University of Science and Technology Pohang 790-784 Korea

Endocytosis and subsequent trafficking pathways are crucial for regulating the activity of plasma membrane-localized proteins. Depending on cellular and physiological conditions, the internalized cargoes are sorted at （and transported from） the trans-Golgi network/early endosome （TGN/EE） to the vacuole for degradation or recycled back to the plasma membrane. How this occurs at the molecular level remains largely elusive. Here, we provide evidence that the ENTH domain-containing protein AtECA4 plays a crucial role in recycling cargoes from the TGN/EE to the plasma membrane in Arabidopsis thaliana. AtECA4：sGFP primarily localized to the TGN/EE and plasma membrane （at low levels）. Upon NaCI or mannitol treatment, AtECA4：sGFP accumulated at the TGN/EE at an early time point but was released from the TGN/EE to the cytosol at later time points. The ateca4mutant showed higher resistance to osmotic stress and more sensitive to exogenous abscisic acid （ABA） than the wild type, as well as increased expres- sion of ABA-inducible genes RD29A and RD29B. Consistently, ABCG25, a plasma membrane-localized ABA exporter, accumulated at the prevacuolar compartment in ateca4, indicating a defect in recycling to the plasma membrane. However, the role of AtECA4 in cargo recycling is not specific to ABCG25, as it also functions in the recycling of BRII. These results suggest that AtECA4 plays a crucial role in the recycling of endocytosed cargoes from the TGN/EE to the plasma membrane.

关键词： abiotic stress A/ENTH cargo recycling

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Molecular Mechanism of the Specificity of Protein Import into Chloroplasts and Mitochondria in Plant Cells

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Molecular Plant 2019年第7期12卷 951-966页

作者： Dong Wook Lee Sumin Lee Junho Lee Seungjin Woo Md.Abdur Razzak Alessandro Vitale inhwan hwang Division of Integrative Biosciences and Biotechnology Pohang University of Science and Technology Pohang 37673 Korea Department of Life Sciences Pohang University of Science and Technology Pohang 37673 Korea Istituto di Biologia e Biotecnologia Agraria Consiglio Nazionale Delle Ricerche Milano Italy

Plants possess both types of endosymbiotic organelles, chloroplasts and mitochondria. Transit peptides and presequences function as signal sequences for specific import into chloroplasts and mitochondria, respectively. However, how these highly similar signal sequences confer the protein import specificity remains elusive. Here, we show that mitochondrial- or chloroplast-specific import involves two distinct steps, specificity determination and translocation across envelopes, which are mediated by the N-terminal regions and functionally interchangeable C-terminal regions, respectively, of transit peptides and presequences. A domain harboring multiple-arginine and hydrophobic sequence motifs in the N-terminal regions of presequences was identified as the mitochondrial specificity factor. The presence of this domain and the absence of arginine residues in the N-terminal regions of otherwise common targeting signals confers specificity of protein import into mitochondria and chloroplasts, respectively. AtToc159, a chloroplast import receptor, also contributes to determining chloroplast import specificity. We propose that common ancestral sequences were functionalized into mitochondrial- and chloroplast-specific signal sequences by the presence and absence, respectively, of multiple-arginine and hydrophobic sequence motifs in the N-terminal region.

关键词： transit peptide presequence protein import into chloroplasts and mitochondria N-terminal specificity domain C-terminal common translocation domain import specificity determination

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Arabidopsis BAG1 Functions as a Cofactor in Hsc70-Mediated Proteasomal Degradation of Unimported Plastid Proteins

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Molecular Plant 2016年第10期9卷 1428-1431页

作者： Dong Wook Lee Su Jin Kim Young Jun Oh Bongsoo Choi Juhun Lee inhwan hwang Division of Integrative Biosciences and Biotechnology Pohang University of Science and Technology Pohang 790-784 Korea

Dear Editor,Eliminating misfolded or mistargeted proteins is crucial for cell viability because these proteins accumulate as non-specific aggregates, which can be toxic to the cell （Lee et al., 2009; Sroka et al., 2009）. Previously, we have shown that in ppi2 （plastid protein import 2） mutant plants, the transcript levels of Hsc70-4 （one isoform of the Hsc70 family） and CHIP （an E3 ligase） were highly upregulated, which ultimately plays crucial roles in proteasomal degradation of unimported plastid proteins （Lee et al., 2009）. We also found that, along with those of Hsc70-4 and CHIP, the transcript level of AtBAG1 （Arabidopsis thaliana Bcl2-associated athanogene 1） in the ppi2 mutant was 2.38-fold higher than that in the wild-type （Lee et al., 2009）.

关键词： SEQUENCE MOTIFS

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Dynamic spatial reorganization of BSK1 complexes in the plasma membrane underpins signal-specific activation for growth and immunity

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Molecular Plant 2021年第4期14卷 588-603页

作者： Bodan Su Xi Zhang Li Li Sammar Abbas Meng Yu Yaning Cui Frantisek Baluska inhwan hwang Xiaoyi Shan Jinxing Lin Beijing Advanced Innovation Center for Tree Breeding by Molecular Design Beijing Forestry UniversityBeijing 100083China College of Biological Sciences&Biotechnology Beijing Forestry UniversityBeijing 100083China lnstitute of Cellular and Molecular Botany University of BonnBonn53115Germany 々Division of Integrative Biosciences and Biotechnology Pohang University of Science and TechnologyPohang37673Korea Present address:School of Life Sciences Tsinghua UniversityBeijing 100084China

Growth and immunity are opposing processes that compete for cellular resources,and proper resource allocation is crucial for plant survival.BSK1 plays a key role in the regulation of both growth and immunity by associating with BRI1 and FLS2,respectively.However,it remains unclear how two antagonistic signals co-opt BSK1 to induce signal-specific activation.Here we show that the dynamic spatial reorganiization of BSK1 within the plasma membrane underlies the mechanism of signal-specific activation for growth or immunity.Resting BSK1 localizes to membrane rafts as complexes.Unlike BSK1-associated FLS2 and BRI1,flg22 or exogenous brassinosteroid(BR)treatment did not decrease BSK1 levels at the plasma membrane(PM)but rather induced BSK1 multimerization and dissociation from FLS2/BSK1 or BRI1/BSK1,respectively.Moreover,flg22-activated BSK1 translocated from membrane rafts to non-membrane-raft regions,whereas BR-activated BSK1 remained in membrane rafts.When applied together with flg22,BR suppressed various flg22-induced BSK1 activities such as BSK1 dissociation from FLS2/BSK1,BSK1 interaction with MAPKKK5,and BSK translocation together with MAPKKK5.Taken together,this study provides a unique insight into how the precise control of BSK1 spatiotemporal organization regulates the signaling specificity to balance plant growth and immunity.

关键词： BSK1 dynamic spatiotemporal organization membrane rafts growth and immunity

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Cytochrome b5 Reductase 1 Triggers Serial Reactions that Lead to Iron Uptake in Plants

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Molecular Plant 2016年第4期9卷 501-513页

作者： Young Jun Oh Hanul Kim Sung Hee Seo Bae Geun hwang Yoon Seok Chang Junho Lee Dong Wook Lee Eun Ju Sohn Sang Joon Lee Youngsook Lee inhwan hwang Division of Integrative Biosciences and Biotechnology Department Life Sciences Division of Environmental Science and Engineering Division of Mechanical Engineering Pohang University of Science and Technology Pohang 790-784 Korea

Rhizosphere acidification is essential for iron （Fe） uptake into plant roots. Plasma membrane （PM） H＊-ATPases play key roles in rhizosphere acidification. However, it is not fully understood how PM H＋-ATPase activity is regulated to enhance root Fe uptake under Fe-deficient conditions. Here, we present evidence that cytochrome b5 reductase 1 （CBR1） increases the levels of unsaturated fatty acids, which stimulate PM H＋-ATPase activity and thus lead to rhizosphere acidification. CBRl-overexpressing （CBRI-OX） Arabidopsis thaliana plants had higher levels of unsaturated fatty acids （18：2 and 18：3）, higher PM H＊-ATPase activity, and lower rhizosphere pH than wild-type plants. By contrast, cbrl loss-of-function mutant plants showed lower levels of unsaturated fatty acids and lower PM H＊-ATPase activity but higher rhizosphere pH. Reduced PM H＊-ATPase activity in cbrl could be restored in vitro by addition of unsatu- rated fatty acids. Transcript levels of CBR1, fatty acids desaturase 2 （FAD2）, and fatty acids desaturase 3 （FAD3） were increased under Fe-deficient conditions. We propose that CBR1 has a crucial role in increasing the levels of unsaturated fatty acids, which activate the PM H＊-ATPase and thus reduce rhizosphere pH. This reaction cascade ultimately promotes root Fe uptake.

关键词： cytochrome b5 reductase 1 （CBR1） unsaturated fatty acids iron （Fe） uptake H^＋-ATPase

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Interactions between Transmembrane Helices within Monomers of the Aquaporin AtPIP2;1 Play a Crucial Role in Tetramer Formation

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Molecular Plant 2016年第7期9卷 1004-1017页

作者： Yun-Joo Yoo Hyun Kyung Lee Wonhee Han Dae Heon Kim Myoung Hui Lee Jouhyun Jeon Dong Wook Lee Junho Lee Yongjik Lee Juhun Lee Jin Seok Kim Yunje Cho Jin-Kwan Han inhwan hwang School of Interdisciplinary Bioscience and Bioengineering Pohang University of Science and Technology Pohang 790-784 Korea Department of Life Sciences Pohang University of Science and Technology Pohang 790-784 Korea Department of Biology Sunchon National University Sunchon 57922 Korea Division of Integrative Biosciences and Biotechnology Pohang University of Science and Technology Pohang 790-784 Korea

Aquaporin （AQP） is a water channel protein found in various subcellular membranes of both prokaryotic and eukaryotic cells. The physiological functions of AQPs have been elucidated in many organisms. However, understanding their biogenesis remains elusive, particularly regarding how they assemble into tetramers. Here, we investigated the amino acid residues involved in the tetramer formation of the Arabidopsis plasma membrane AQP AtPIP2;1 using extensive amino acid substitution mutagenesis. The mutant proteins V41A/ E44A, F51A/L52A, F87A/191A, F92A/193A, V95A/Y96A, and H216A/L217A, harboring alanine substitutions in the transmembrane （TM） helices of AtPIP2;1 polymerized into multiple oligomeric complexes with a vari- able number of subunits greater than four. Moreover, these mutant proteins failed to traffic to the plasma membrane, instead of accumulating in the endoplasmic reticulum （ER）. Structure-based modeling revealed that these residues are largely involved in interactions between TM helices within monomers. These results suggest that inter-TM interactions occurring both within and between monomers play crucial roles in tetramer formation in the AtPIP2;1 complex. Moreover, the assembly of AtPIP2;1 tetramers is critical for their trafficking from the ER to the plasma membrane, as well as water permeability.

关键词： aquaporin AtPIP2 tetramer formation interaction between transmembrane helices

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