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Hrmova M, Zimmer J, Bulone V, Fincher GB. Enzymes in 3D: Synthesis, remodelling, and hydrolysis of cell wall (1,3;1,4)-β-glucans. PLANT PHYSIOLOGY 2023; 194:33-50. [PMID: 37594400 PMCID: PMC10762513 DOI: 10.1093/plphys/kiad415] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2023] [Accepted: 06/09/2023] [Indexed: 08/19/2023]
Abstract
Recent breakthroughs in structural biology have provided valuable new insights into enzymes involved in plant cell wall metabolism. More specifically, the molecular mechanism of synthesis of (1,3;1,4)-β-glucans, which are widespread in cell walls of commercially important cereals and grasses, has been the topic of debate and intense research activity for decades. However, an inability to purify these integral membrane enzymes or apply transgenic approaches without interpretative problems associated with pleiotropic effects has presented barriers to attempts to define their synthetic mechanisms. Following the demonstration that some members of the CslF sub-family of GT2 family enzymes mediate (1,3;1,4)-β-glucan synthesis, the expression of the corresponding genes in a heterologous system that is free of background complications has now been achieved. Biochemical analyses of the (1,3;1,4)-β-glucan synthesized in vitro, combined with 3-dimensional (3D) cryogenic-electron microscopy and AlphaFold protein structure predictions, have demonstrated how a single CslF6 enzyme, without exogenous primers, can incorporate both (1,3)- and (1,4)-β-linkages into the nascent polysaccharide chain. Similarly, 3D structures of xyloglucan endo-transglycosylases and (1,3;1,4)-β-glucan endo- and exohydrolases have allowed the mechanisms of (1,3;1,4)-β-glucan modification and degradation to be defined. X-ray crystallography and multi-scale modeling of a broad specificity GH3 β-glucan exohydrolase recently revealed a previously unknown and remarkable molecular mechanism with reactant trajectories through which a polysaccharide exohydrolase can act with a processive action pattern. The availability of high-quality protein 3D structural predictions should prove invaluable for defining structures, dynamics, and functions of other enzymes involved in plant cell wall metabolism in the immediate future.
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Affiliation(s)
- Maria Hrmova
- School of Agriculture, Food and Wine, and the Waite Research Institute, University of Adelaide, Glen Osmond, South Australia 5064, Australia
| | - Jochen Zimmer
- Howard Hughes Medical Institute and Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
| | - Vincent Bulone
- College of Medicine and Public Health, Flinders University, Bedford Park, South Australia 5042, Australia
- Division of Glycoscience, Department of Chemistry, KTH Royal Institute of Technology, Alba Nova University Centre, 106 91 Stockholm, Sweden
| | - Geoffrey B Fincher
- School of Agriculture, Food and Wine, and the Waite Research Institute, University of Adelaide, Glen Osmond, South Australia 5064, Australia
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Stratilová B, Šesták S, Stratilová E, Vadinová K, Kozmon S, Hrmova M. Engineering of substrate specificity in a plant cell-wall modifying enzyme through alterations of carboxyl-terminal amino acid residues. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2023; 116:1529-1544. [PMID: 37658783 DOI: 10.1111/tpj.16435] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Revised: 08/07/2023] [Accepted: 08/12/2023] [Indexed: 09/05/2023]
Abstract
Structural determinants of substrate recognition remain inadequately defined in broad specific cell-wall modifying enzymes, termed xyloglucan xyloglucosyl transferases (XETs). Here, we investigate the Tropaeolum majus seed TmXET6.3 isoform, a member of the GH16_20 subfamily of the GH16 network. This enzyme recognises xyloglucan (XG)-derived donors and acceptors, and a wide spectrum of other chiefly saccharide substrates, although it lacks the activity with homogalacturonan (pectin) fragments. We focus on defining the functionality of carboxyl-terminal residues in TmXET6.3, which extend acceptor binding regions in the GH16_20 subfamily but are absent in the related GH16_21 subfamily. Site-directed mutagenesis using double to quintuple mutants in the carboxyl-terminal region - substitutions emulated on barley XETs recognising the XG/penta-galacturonide acceptor substrate pair - demonstrated that this activity could be gained in TmXET6.3. We demonstrate the roles of semi-conserved Arg238 and Lys237 residues, introducing a net positive charge in the carboxyl-terminal region (which complements a negative charge of the acidic penta-galacturonide) for the transfer of xyloglucan fragments. Experimental data, supported by molecular modelling of TmXET6.3 with the XG oligosaccharide donor and penta-galacturonide acceptor substrates, indicated that they could be accommodated in the active site. Our findings support the conclusion on the significance of positively charged residues at the carboxyl terminus of TmXET6.3 and suggest that a broad specificity could be engineered via modifications of an acceptor binding site. The definition of substrate specificity in XETs should prove invaluable for defining the structure, dynamics, and function of plant cell walls, and their metabolism; these data could be applicable in various biotechnologies.
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Affiliation(s)
- Barbora Stratilová
- Institute of Chemistry, Slovak Academy of Sciences, SK-84538, Bratislava, Slovakia
| | - Sergej Šesták
- Institute of Chemistry, Slovak Academy of Sciences, SK-84538, Bratislava, Slovakia
| | - Eva Stratilová
- Institute of Chemistry, Slovak Academy of Sciences, SK-84538, Bratislava, Slovakia
| | - Kristína Vadinová
- Institute of Chemistry, Slovak Academy of Sciences, SK-84538, Bratislava, Slovakia
| | - Stanislav Kozmon
- Institute of Chemistry, Slovak Academy of Sciences, SK-84538, Bratislava, Slovakia
| | - Maria Hrmova
- School of Agriculture, Food and Wine & Waite Research Institute, University of Adelaide, Waite Research Precinct, Glen Osmond, South Australia, 5064, Australia
- Jiangsu Collaborative Innovation Centre for Regional Modern Agriculture and Environmental Protection, School of Life Science, Huaiyin Normal University, Huai'an, 223300, China
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Yang L, Chen Y, Liu X, Zhang S, Han Q. Genome-wide identification and expression analysis of xyloglucan endotransglucosylase/hydrolase genes family in Salicaceae during grafting. BMC Genomics 2023; 24:676. [PMID: 37946112 PMCID: PMC10636897 DOI: 10.1186/s12864-023-09762-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2023] [Accepted: 10/23/2023] [Indexed: 11/12/2023] Open
Abstract
BACKGROUND Poplar (Populus cathayana)and willow (Salix rehderiana) are important fast-growing trees in China. Grafting plays an important role in improving plant stress resistance and construction of ornamental plants. It is found that willow scions grafted onto poplar rootstocks can form ornamental plants. However, this grafted combination has a low survival rate. Many studies have reported that the xyloglucan endotransglucosylase/hydrolase (XTH) family plays an important role in the healing process of grafts. RESULTS A total of 38 PtrXTHs and 32 SpuXTHs were identified in poplar and willow respectively, and were classified into three subfamilies. Tandem duplication was the main reason for the expansion of the PtrXTHs. Grafting treatment and Quantitative real time PCR (RT-qPCR) analysis revealed that five XTH genes differentially expressed between self-grafted and reciprocal grafted combinations. Specifically, the high expression levels of SrXTH16, SrXTH17, SrXTH25, PcXTH22 and PcXTH17 may contribute to the high survival rate of the grafted combination with willow scion and poplar rootstock. Subcellular localization identified that the SrXTH16, SrXTH17, SrXTH25, PcXTH17 and PcXTH22 proteins were located on the cell walls. Transcription factors (NAC, MYB and DOF) may regulate the five XTH genes. CONCLUSIONS This study provides a new understanding of the roles of PcXTH and SrXTH genes and their roles in grafting. Our results will give some hints to explore the molecular mechanisms of PcXTH and SrXTH genes involved in grafting in the future.
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Affiliation(s)
- Le Yang
- Key Laboratory of Bio-Resource and Eco-Environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu, 610065, China
| | - Yao Chen
- Key Laboratory of Bio-Resource and Eco-Environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu, 610065, China
| | - Xuejiao Liu
- Key Laboratory of Bio-Resource and Eco-Environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu, 610065, China
| | - Sheng Zhang
- Key Laboratory of Bio-Resource and Eco-Environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu, 610065, China
| | - Qingquan Han
- Key Laboratory of Bio-Resource and Eco-Environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu, 610065, China.
- The Engineering Research Institute of Agriculture and Forestry, Ludong University, 186 Hongqizhong Road, Yantai, 264025, Shandong Province, China.
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Stratilová B, Stratilová E, Hrmova M, Kozmon S. Definition of the Acceptor Substrate Binding Specificity in Plant Xyloglucan Endotransglycosylases Using Computational Chemistry. Int J Mol Sci 2022; 23:ijms231911838. [PMID: 36233140 PMCID: PMC9569819 DOI: 10.3390/ijms231911838] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2022] [Revised: 09/27/2022] [Accepted: 09/28/2022] [Indexed: 11/16/2022] Open
Abstract
Xyloglucan endotransglycosylases (XETs) play key roles in the remodelling and reconstruction of plant cell walls. These enzymes catalyse homo-transglycosylation reactions with xyloglucan-derived donor and acceptor substrates and hetero-transglycosylation reactions with a variety of structurally diverse polysaccharides. In this work, we describe the basis of acceptor substrate binding specificity in non-specific Tropaeolum majus (TmXET6.3) and specific Populus tremula x tremuloides (PttXET16A) XETs, using molecular docking and molecular dynamics (MD) simulations combined with binding free energy calculations. The data indicate that the enzyme-donor (xyloglucan heptaoligosaccharide or XG-OS7)/acceptor complexes with the linear acceptors, where a backbone consisted of glucose (Glc) moieties linked via (1,4)- or (1,3)-β-glycosidic linkages, were bound stably in the active sites of TmXET6.3 and PttXET16A. Conversely, the acceptors with the (1,6)-β-linked Glc moieties were bound stably in TmXET6.3 but not in PttXET16A. When in the (1,4)-β-linked Glc containing acceptors, the saccharide moieties were replaced with mannose or xylose, they bound stably in TmXET6.3 but lacked stability in PttXET16A. MD simulations of the XET-donor/acceptor complexes with acceptors derived from (1,4;1,3)-β-glucans highlighted the importance of (1,3)-β-glycosidic linkages and side chain positions in the acceptor substrates. Our findings explain the differences in acceptor binding specificity between non-specific and specific XETs and associate theoretical to experimental data.
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Affiliation(s)
- Barbora Stratilová
- Institute of Chemistry, Slovak Academy of Sciences, SK-84538 Bratislava, Slovakia
| | - Eva Stratilová
- Institute of Chemistry, Slovak Academy of Sciences, SK-84538 Bratislava, Slovakia
| | - Maria Hrmova
- Jiangsu Collaborative Innovation Centre for Regional Modern Agriculture and Environmental Protection, School of Life Science, Huaiyin Normal University, Huai’an 223300, China
- School of Agriculture, Food and Wine & Waite Research Institute, University of Adelaide, Glen Osmond, SA 5064, Australia
- Correspondence: (M.H.); (S.K.)
| | - Stanislav Kozmon
- Institute of Chemistry, Slovak Academy of Sciences, SK-84538 Bratislava, Slovakia
- Medical Vision o.z., SK-82108 Bratislava, Slovakia
- Correspondence: (M.H.); (S.K.)
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Ishida K, Yokoyama R. Reconsidering the function of the xyloglucan endotransglucosylase/hydrolase family. JOURNAL OF PLANT RESEARCH 2022; 135:145-156. [PMID: 35000024 DOI: 10.1007/s10265-021-01361-w] [Citation(s) in RCA: 23] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Accepted: 11/21/2021] [Indexed: 05/21/2023]
Abstract
Plants possess an outer cell layer called the cell wall. This matrix comprises various molecules, such as polysaccharides and proteins, and serves a wide array of physiologically important functions. This structure is not static but rather flexible in response to the environment. One of the factors responsible for this plasticity is the xyloglucan endotransglucosylase/hydrolase (XTH) family, which cleaves and reconnects xyloglucan molecules. Since xyloglucan molecules have been hypothesised to tether cellulose microfibrils forming the main load-bearing network in the primary cell wall, XTHs have been thought to play a central role in cell wall loosening for plant cell expansion. However, multiple lines of recent evidence have questioned this classic model. Nevertheless, reverse genetic analyses have proven the biological importance of XTHs; therefore, a major challenge at present is to reconsider the role of XTHs in planta. Recent advances in analytical techniques have allowed for gathering rich information on the structure of the primary cell wall. Thus, the integration of accumulated knowledge in current XTH studies may offer a turning point for unveiling the precise functions of XTHs. In the present review, we redefine the biological function of the XTH family based on the recent architectural model of the cell wall. We highlight three key findings regarding this enzyme family: (1) XTHs are not strictly required for cell wall loosening during plant cell expansion but play vital roles in response to specific biotic or abiotic stresses; (2) in addition to their transglycosylase activity, the hydrolase activity of XTHs is involved in physiological benefits; and (3) XTHs can recognise a wide range of polysaccharides other than xyloglucans.
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Affiliation(s)
- Konan Ishida
- Department of Biochemistry, University of Cambridge, Cambridge, CB2 1QE, UK
| | - Ryusuke Yokoyama
- Graduate School of Life Sciences, Tohoku University, Sendai, 980-8578, Japan.
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Behar H, Samuels AL, Brumer H. Physcomitrium (Physcomitrella) patens endo-glucanase 16 is involved in the cell wall development of young tissue. PHYSIOLOGIA PLANTARUM 2022; 174:e13683. [PMID: 35396710 DOI: 10.1111/ppl.13683] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2022] [Revised: 03/22/2022] [Accepted: 04/04/2022] [Indexed: 06/14/2023]
Abstract
Plants maintain large repertoires of carbohydrate-active enzymes (CAZymes)-comprising between 3% and 10% of their genomes-to synthesize, modify, and degrade the polysaccharide components of the cell wall. We recently identified a unique group of plant endo-glucanases from Glycoside Hydrolase Family 16, viz. EG16 orthologs, which constitute a sister clade to the well-known XYLOGLUCAN ENDO-TRANSGLYCOSYLASE/HYDROLASE (XTH) gene products. Biochemical analysis of EG16 orthologs from poplar (Populus trichocarpa), grapevine (Vitis vinifera), and spreading earthmoss (Physcomitrium patens) has demonstrated that these endo-glucanases are distinctly active on cell wall matrix glycans, mixed-linkage β(1,3);β(1,4)-glucan and xyloglucan (XyG), and that enzyme structure and specificity is highly conserved across diverse plant lineages. However, the physiological role of EG16 orthologs in any species is presently unknown. To shed light on EG16 function in vivo, here we performed reverse genetics and protein localization analyses of the single EG16 ortholog in the model moss P. patens, where this gene is highly expressed in young, expanding tissues, particularly in protonema. Surprisingly, deletion of the PpEG16 gene by homologous recombination led to an increase in growth, as well as accelerated senescence. Notably, the PpEG16 protein was shown to co-localize with XyG in the cell wall of protonema tissue, specifically at cell tips, despite lacking a secretion signal peptide. Although the precise biological role of EG16 orthologs remains elusive, our results implicate these highly conserved glycoside hydrolases in cell wall polysaccharide remodeling and recycling. We anticipate that these foundational results will inform future studies on EG16 function across plant lineages.
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Affiliation(s)
- Hila Behar
- Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Biochemistry and Molecular Biology, Life Sciences Centre, University of British Columbia, Vancouver, British Columbia, Canada
| | - Anne Lacey Samuels
- Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada
| | - Harry Brumer
- Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Biochemistry and Molecular Biology, Life Sciences Centre, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada
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Hrmova M, Stratilová B, Stratilová E. Broad Specific Xyloglucan:Xyloglucosyl Transferases Are Formidable Players in the Re-Modelling of Plant Cell Wall Structures. Int J Mol Sci 2022; 23:ijms23031656. [PMID: 35163576 PMCID: PMC8836008 DOI: 10.3390/ijms23031656] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Revised: 01/25/2022] [Accepted: 01/26/2022] [Indexed: 01/27/2023] Open
Abstract
Plant xyloglucan:xyloglucosyl transferases, known as xyloglucan endo-transglycosylases (XETs) are the key players that underlie plant cell wall dynamics and mechanics. These fundamental roles are central for the assembly and modifications of cell walls during embryogenesis, vegetative and reproductive growth, and adaptations to living environments under biotic and abiotic (environmental) stresses. XET enzymes (EC 2.4.1.207) have the β-sandwich architecture and the β-jelly-roll topology, and are classified in the glycoside hydrolase family 16 based on their evolutionary history. XET enzymes catalyse transglycosylation reactions with xyloglucan (XG)-derived and other than XG-derived donors and acceptors, and this poly-specificity originates from the structural plasticity and evolutionary diversification that has evolved through expansion and duplication. In phyletic groups, XETs form the gene families that are differentially expressed in organs and tissues in time- and space-dependent manners, and in response to environmental conditions. Here, we examine higher plant XET enzymes and dissect how their exclusively carbohydrate-linked transglycosylation catalytic function inter-connects complex plant cell wall components. Further, we discuss progress in technologies that advance the knowledge of plant cell walls and how this knowledge defines the roles of XETs. We construe that the broad specificity of the plant XETs underscores their roles in continuous cell wall restructuring and re-modelling.
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Affiliation(s)
- Maria Hrmova
- Jiangsu Collaborative Innovation Centre for Regional Modern Agriculture and Environmental Protection, School of Life Science, Huaiyin Normal University, Huai’an 223300, China
- School of Agriculture, Food and Wine & Waite Research Institute, University of Adelaide, Glen Osmond, SA 5064, Australia
- Correspondence: ; Tel.: +61-8-8313-0775
| | - Barbora Stratilová
- Institute of Chemistry, Centre for Glycomics, Slovak Academy of Sciences, SK-84538 Bratislava, Slovakia; (B.S.); (E.S.)
- Faculty of Natural Sciences, Department of Physical and Theoretical Chemistry, Comenius University, SK-84215 Bratislava, Slovakia
| | - Eva Stratilová
- Institute of Chemistry, Centre for Glycomics, Slovak Academy of Sciences, SK-84538 Bratislava, Slovakia; (B.S.); (E.S.)
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