Protocols for isolating and characterizing polysaccharides from plant cell walls: a case study using rhamnogalacturonan-II

An in-depth review: Unraveling the extraction, structure, bio-functionalities, target molecules, and applications of pectic polysaccharides

Pectic polysaccharides have long been a challenging subject of research in the field of macromolecular science, given their complex structures and wide range of biological effects. However, the extensive exploration of pectic polysaccharides has been limited due to the intricacy of their structures. In this comprehensive review, we aim to provide a thorough summary of the existing knowledge on pectic polysaccharides, with a particular focus on aspects such as classification, extraction methodologies, structural analysis, elucidation of biological activities, and exploration of target molecules and signaling pathways. By conducting a comprehensive analysis of existing literature and research achievements, we strive to establish a comprehensive and systematic framework that can serve as a reference and guide for further investigations into pectic polysaccharides. Furthermore, this review delves into the applications of pectic polysaccharides beyond their fundamental attributes and characteristics, exploring their potential in fields such as materials, food, and pharmaceuticals. We pay special attention to the promising opportunities for pectic polysaccharides in the pharmaceutical domain and provide an overview of related drug development research. The aim of this review is to facilitate a holistic understanding of pectic polysaccharides by incorporating multifaceted research, providing valuable insights for further in-depth investigations into this significant polymer.

Putative rhamnogalacturonan-II glycosyltransferase identified through callus gene editing which bypasses embryo lethality

Rhamnogalacturonan II (RG-II) is a structurally complex and conserved domain of the pectin present in the primary cell walls of vascular plants. Borate cross-linking of RG-II is required for plants to grow and develop normally. Mutations that alter RG-II structure also affect cross-linking and are lethal or severely impair growth. Thus, few genes involved in RG-II synthesis have been identified. Here, we developed a method to generate viable loss-of-function Arabidopsis (Arabidopsis thaliana) mutants in callus tissue via CRISPR/Cas9-mediated gene editing. We combined this with a candidate gene approach to characterize the male gametophyte defective 2 (MGP2) gene that encodes a putative family GT29 glycosyltransferase. Plants homozygous for this mutation do not survive. We showed that in the callus mutant cell walls, RG-II does not cross-link normally because it lacks 3-deoxy-D-manno-octulosonic acid (Kdo) and thus cannot form the α-L-Rhap-(1→5)-α-D-kdop-(1→sidechain). We suggest that MGP2 encodes an inverting RG-II CMP-β-Kdo transferase (RCKT1). Our discovery provides further insight into the role of sidechains in RG-II dimerization. Our method also provides a viable strategy for further identifying proteins involved in the biosynthesis of RG-II.

In vivo and ex vivo study on cell wall components as part of the network in tomato fruit during the ripening process

Ripening is a process involving various morphological, physiological, and biochemical changes in fruits. This process is affected by modifications in the cell wall structure, particularly in the composition of polysaccharides and proteins. The cell wall assembly is a network of polysaccharides and proteoglycans named the arabinoxylan pectin arabinogalactan protein1 (APAP1). The complex consists of the arabinogalactan protein (AGP) core with the pectin domain including arabinogalactan (AG) type II, homogalacturonan (HG), and rhamnogalacturonan I (RG-I). The present paper aims to determine the impact of a disturbance in the synthesis of one constituent on the integrity of the cell wall. Therefore, in the current work, we have tested the impact of modified expression of the SlP4H3 gene connected with proline hydroxylase (P4H) activity on AGP presence in the fruit matrix. Using an immunolabelling technique (CLSM), an immunogold method (TEM), molecular tools, and calcium mapping (SEM-EDS), we have demonstrated that disturbances in AGP synthesis affect the entire cell wall structure. Changes in the spatio-temporal AGP distribution may be related to the formation of a network between AGPs with other cell wall components. Moreover, the modified structure of the cell wall assembly induces morphological changes visible at the cellular level during the progression of the ripening process. These results support the hypothesis that AGPs and pectins are required for the proper progression of the physiological processes occurring in fruits.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2021-2022

The use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of carbohydrates and glycoconjugates is a well-established technique and this review is the 12th update of the original article published in 1999 and brings coverage of the literature to the end of 2022. As with previous review, this review also includes a few papers that describe methods appropriate to analysis by MALDI, such as sample preparation, even though the ionization method is not MALDI. The review follows the same format as previous reviews. It is divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of computer software for structural identification. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other general areas such as medicine, industrial processes, natural products and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. MALDI is still an ideal technique for carbohydrate analysis, particularly in its ability to produce single ions from each analyte and advancements in the technique and range of applications show little sign of diminishing.

Variation pattern in the macromolecular (cellulose, hemicelluloses, lignin) composition of cell walls in Pinus tabulaeformis tree trunks at different ages as revealed using multiple techniques

The plant cell wall is a complex, heterogeneous structure primarily composed of cellulose, hemicelluloses, and lignin. Exploring the variations in these three macromolecules over time is crucial for understanding wood formation to enhance chemical processing and utilization. Here, we comprehensively analyzed the chemical composition of cell walls in the trunks of Pinus tabulaeformis using multiple techniques. In situ analysis showed that macromolecules accumulated gradually in the cell wall as the plant aged, and the distribution pattern of lignin was opposite that of polysaccharides, and both showed heterogenous distribution patterns. In addition, gel permeation chromatography (GPC) results revealed that the molecular weights of hemicelluloses decreased while that of lignin increased with age. Two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance (2D-HSQC NMR) analysis indicated that hemicelluloses mainly comprised galactoglucomannan and arabinoglucuronoxylan, and the lignin types were mainly comprised guaiacyl (G) and p-hydroxyphenyl (H) units with three main linkage types: β-O-4, β-β, and β-5. Furthermore, the C-O bond (β-O-4) signals of lignin decreased while the C-C bonds (β-β and β-5) signals increased over time. Taken together, these findings shed light on wood formation in P. tabulaeformis and lay the foundation for enhancing the processing and use of wood and timber products.

Pectic-AGP is a major form of Arabidopsis AGPs

As a key component in cell walls of numerous organisms ranging from green algae to higher plants, AGPs play principal roles in many biological processes such as cell-cell adhesion and regulating Ca2+ signaling pathway as a Ca2+-capacitor. Consistently, AGP structures vary from species to species and from tissue to tissue. To understand the functions of AGPs, it is vital to know their structural differences relative to their location in the plant. Thus, AGPs were purified from different Arabidopsis tissues. Analyses of these AGPs demonstrated that the AGPs comprised covalently linked pectin and AGP, referred to as pectic-AGPs. Importantly, these pectic-AGPs were glycosylated with a remarkable variety of polysaccharides including homogalacturonan, rhamnogalacturonan-I, and type II arabinogalactan at different ratios and lengths. This result not only suggests that pectic-AGP is a major form of Arabidopsis AGPs, but also supports AGPs serve as crosslinkers covalently connecting pectins with structures tailored for tissue-specific functions.

Streamlining assays of glycosyltransferases activity using in vitro GT-array (i-GT-ray) platform: Application to family GT37 fucosyltransferases

Numerous putative glycosyltransferases (GTs) have been identified using bioinformatic approaches. However, demonstrating the activity of these GTs remains a challenge. Here, we describe the development of a rapid in vitro GT-array screening platform for activity of GTs. GT-arrays are generated by cell-free in vitro protein synthesis and binding using microplates precoated with a N-terminal Halo- or a C-terminal GST-tagged GT-encoding plasmid DNA and a capture antibody. These arrays are then used for screening of transferase activities and the reactions are monitored by a luminescence GLO assay. The products formed by these reactions can be analyzed directly from the microplates by mass spectrometry. Using this platform, a total of 280 assays were performed to screen 22 putative fucosyltransferases (FUTs) from family GT37 (seven from Arabidopsis and 15 from rice) for activity toward five acceptors: non-fucosylated tamarind xyloglucan (TXyG), arabinotriose (Ara3), non-fucosylated rhamnogalacturonan I (RG-I), and RG-II from the mur1-1 Arabidopsis mutant, and the celery RG-II monomer lacking Arap and MeFuc of chain B and l-Gal of chain A. Our screen showed that AtFUT2, AtFUT5, and AtFUT10 have activity toward RG-I, while AtFUT8 was active on RG-II. Five rice OsFUTs have XyG-FUT activity and four rice OsFUTs have activity toward Ara3. None of the putative OsFUTs were active on the RG-I and RG-II. However, promiscuity toward acceptors was observed for several FUTs. These findings extend our knowledge of cell wall polysaccharide fucosylation in plants. We believe that in vitro GT-array platform provides a valuable tool for cell wall biochemistry and other research fields.

Sequence, structure and functionality of pectin methylesterases and their use in sustainable carbohydrate bioproducts: A review

Pectin methylesterases (PMEs) are enzymes that play a critical role in modifying pectins, a class of complex polysaccharides in plant cell walls. These enzymes catalyze the removal of methyl ester groups from pectins, resulting in a change in the degree of esterification and consequently, the physicochemical properties of the polymers. PMEs are found in various plant tissues and organs, and their activity is tightly regulated in response to developmental and environmental factors. In addition to the biochemical modification of pectins, PMEs have been implicated in various biological processes, including fruit ripening, defense against pathogens, and cell wall remodelling. This review presents updated information on PMEs, including their sources, sequences and structural diversity, biochemical properties and function in plant development. The article also explores the mechanisms of PME action and the factors influencing enzyme activity. In addition, the review highlights the potential applications of PMEs in various industrial sectors related to biomass exploitation, food, and textile industries, with a focus on development of bioproducts based on eco-friendly and efficient industrial processes.

Naturally and chemically acetylated polysaccharides: Structural characteristics, synthesis, activities, and applications in the delivery system: A review

Acetylated polysaccharides refer to polysaccharides containing acetyl groups on sugar units. In the past, the acetylation modification of wall polysaccharides has been a hot research topic for scientists. However, in recent years, many studies have reported that acetylation-modified plant, animal, and microbial polysaccharide show great potential in delivery systems. From the latest perspective, this review systematically presents the different sources of naturally acetylated polysaccharides, the regularity of their modification, the chemical preparation of acetylation modifications, the biological activities and functions of acetylated polysaccharides, and the application in the delivery system. In nature, acetylated polysaccharides are extensively distributed in plants, microorganism, and animals. The level of acetylation modification, the distribution of chains, and the locations of acetylation modification sites differ between species. An increasing number of acetylated polysaccharides were prepared in the aqueous medium, which is safe, environment friendly, and low-cost. In addition to being necessary for plant growth and development, acetylated polysaccharides have immunomodulatory, antioxidant, and anticancer properties. The above-mentioned multiple sources, multifunctional and multi-active acetylated polysaccharides, make them an increasingly important part of delivery systems. We conclude by discussing the future directions for research and development and the potential uses for acetylated polysaccharides.

Insights into pectin O-acetylation in the plant cell wall: structure, synthesis, and modification

O-Acetyl esterification is an important structural and functional feature of pectins present in the cell walls of all land plants. The amount and positions of pectin acetyl substituents varies across plant tissues and stages of development. Plant growth and response to biotic and abiotic stress are known to be significantly influenced by pectin O-acetylation. Gel formation is a key characteristic of pectins, and many studies have shown that gel formation is dependent upon the degree of acetylation. Previous studies have indicated that members of the TRICHOME BIREFRINGENCE-LIKE (TBL) family may play a role in the O-acetylation of pectin, however, biochemical evidence for acceptor specific pectin acetyltransferase activity remains to be confirmed and the exact mechanism(s) for catalysis must be determined. Pectin acetylesterases (PAEs) affect pectin acetylation as they hydrolyze acetylester bonds and have a role in the amount and distribution of O-acetylation. Several mutant studies suggest the critical role of pectin O-acetylation; however, additional research is required to fully understand this. This review aims to discuss the importance, role, and putative mechanism of pectin O-acetylation.

Polymerization of the backbone of the pectic polysaccharide rhamnogalacturonan I

Rhamnogalacturonan I (RG-I) is a major plant cell wall pectic polysaccharide defined by its repeating disaccharide backbone structure of [4)-α-D-GalA-(1,2)-α-L-Rha-(1,]. A family of RG-I:Rhamnosyltransferases (RRT) has previously been identified, but synthesis of the RG-I backbone has not been demonstrated in vitro because the identity of Rhamnogalacturonan I:Galaturonosyltransferase (RG-I:GalAT) was unknown. Here a putative glycosyltransferase, At1g28240/MUCI70, is shown to be an RG-I:GalAT. The name RGGAT1 is proposed to reflect the catalytic activity of this enzyme. When incubated together with the rhamnosyltransferase RRT4, the combined activities of RGGAT1 and RRT4 result in elongation of RG-I acceptors in vitro into a polymeric product. RGGAT1 is a member of a new GT family categorized as GT116, which does not group into existing GT-A clades and is phylogenetically distinct from the GALACTURONOSYLTRANSFERASE (GAUT) family of GalA transferases that synthesize the backbone of the pectin homogalacturonan. RGGAT1 has a predicted GT-A fold structure but employs a metal-independent catalytic mechanism that is rare among glycosyltransferases with this fold type. The identification of RGGAT1 and the 8-member Arabidopsis GT116 family provides a new avenue for studying the mechanism of RG-I synthesis and the function of RG-I in plants.

Polysaccharide Regulation of Intestinal Flora: A Viable Approach to Maintaining Normal Cognitive Performance and Treating Depression

The intestinal tract of a healthy body is home to a large variety and number of microorganisms that will affect every aspect of the host’s life. In recent years, polysaccharides have been found to be an important factor affecting intestinal flora. Polysaccharides are widely found in nature and play a key role in the life activities of living organisms. In the intestinal tract of living organisms, polysaccharides have many important functions, such as preventing the imbalance of intestinal flora and maintaining the integrity of the intestinal barrier. Moreover, recent studies suggest that gut microbes can influence brain health through the brain-gut axis. Therefore, maintaining brain health through polysaccharide modulation of gut flora deserves further study. In this review, we outline the mechanisms by which polysaccharides maintain normal intestinal flora structure, as well as improving cognitive function in the brain via the brain-gut axis by virtue of the intestinal flora. We also highlight the important role that gut microbes play in the pathogenesis of depression and the potential for treating depression through the use of polysaccharides to modulate the intestinal flora.