Electrophoretic Behavior of Copolymeric Galacturonans Including Comments on the Information Content of the Intermolecular Charge Distribution

Biotinylation of reducing and non-reducing termini to create plug-and-play polysaccharides

Single-molecule studies continue to grow in popularity. In cases where biopolymer samples of interest exhibit variations in fine-structure between individual chains such single-molecule studies uniquely offer the promise of revealing deep structure-function relationships. Polysaccharides are typically studied in bulk and, as such, their study could greatly benefit from the application of single-molecule techniques. However, while for example single-molecule optical tweezers (OT) studies have become commonplace for DNA, studies of polysaccharides have lagged behind somewhat, complicated by the difficulty of studying molecules that amongst other things have more complex end-group chemistry. Recently, divalent streptavidin linkers have been shown to be capable of concatenating two pieces of biotin-terminated DNA to produce robust composite strings that run intact through conventional gels, and can be used in single-molecule OT experiments (Mohandas, Kent, Raudsepp, Jameson, & Williams, 2022). By using two such streptavidin linkers, biotin-terminated polymers could be inserted between two sections of DNA in order to facilitate single-molecule experiments on biopolymers that are currently difficult to address by other means. Here, we describe a generic approach for placing the required biotin moieties at both ends of polysaccharide chains, producing plug-and-play polysaccharide inserts that can be incorporated into composite polymer strings using streptavidin linking hubs.

Pectic hydrocolloids from steam-exploded lime pectin peel: Effect of temperature and time on macromolecular and functional properties

Previously, we showed the weight average molecular weight (M w) and intrinsic viscosity ([ƞ]) of pectic hydrocolloids recovered from steam-exploded citrus peel were low, suggesting fragmentation due to process temperature and/or time-at-temperature. We have tested this hypothesis on a commercial lime pectin peel, washed to remove soluble sugars and dried for stabilization, using a static steam explosion system. We examined temperatures of 120-150°C at 1-3 min hold times. Galacturonic acid recovery and M w ranged from 22% to 82% and 142-214 kDa, respectively. Recovery of most major pectic sugars increased concomitantly with galacturonic acid as temperature and time-at-temperature increased. [ƞ] ranged from 1.75 to 6.83 dl/g. The degree of methylesterification ranged from 66.5% to 72.1%. Tan (δ) (Loss modulus/Storage modulus; G″/G') values of sugar-acid gels for 120-140°C treatments were <1.0. Ideal optimization analysis, where time, [ƞ], and percent recovery were maximized, identified processing conditions that favor either increased [ƞ] or percent recovery. The results presented here support our hypothesis that temperature and time-at-temperature affect M w and [η] of the recovered pectic hydrocolloids. These results also demonstrate that manipulating either temperature or time-at-temperature enables the production of structurally varied populations of pectic hydrocolloids. Based on optimization analysis, commercially viable values of [ƞ] can be obtained while recovering approximately 50% of the pectic hydrocolloids.

The Effect of Different Extraction Conditions on the Physical Properties, Conformation and Branching of Pectins Extracted from Cucumis melo Inodorus

The extraction of pectin involves the physico-chemical hydrolysis and solubilisation of pectic polymers from plant tissues under the influence of several processing parameters. In this study, an experimental design approach was used to examine the effects of extraction pH, time and temperature on the pectins extracted from Cucumis melo Inodorus. Knowledge of physical properties (intrinsic viscosity and molar mass), dilute solution conformation (persistence length and mass per unit length), together with chemical composition, was then used to propose a new method, which can estimate the length and number of branches on the pectin RG-I region. The results show that physical properties, conformation and the length and number of branches are sensitive to extraction conditions. The fitting of regression equations relating length and number of branches on the pectin RG-I region to extraction conditions can, therefore, lead to tailor-made pectins with specific properties for specific applications.

On the electrophoretic mobilities of partially charged oligosaccharides as a function of charge patterning and degree of polymerization

Fully or partially charged oligosaccharide molecules play a key role in many areas of biology, where their fine structures are crucial in determining their functionality. However, the separation of specific charged oligosaccharides from similar moieties that typically coexist in extracted samples, even for those that are unbranched, and in cases where each saccharide moiety can only carry a single charge or not, is far from trivial. Typically such molecules are characterized by a degree of polymerization n and a number m (and distribution) of charged residues, and must be separated from a plethora of similar species possessing different combinations of n and m. Furthermore, the separation of the possible n!/m!(n-m)! isomers of each species of fixed n and m is a formidable challenge to analytical chemists. Herein, we report the results of molecular dynamics simulations that have been performed in order to calculate the free solution electrophoretic mobilities of galacturonides and charged oligosaccharides derived from digests of the important plant cell-wall polysaccharide pectin. The simulations are compared with an experiment and are found to correctly predict the loss of resolution of fully charged species above a critical degree of polymerization n and the ionic strength dependence of the electrophoretic mobilities of different partially charged oligosaccharides. It is expected that having a predictive tool for the calculation of the electrophoretic mobilities of differently charged oligosaccharide species in hand will allow experimental conditions that optimize the resolution of particular species to be ascertained and understood.

β-Lactoglobulin nanofibrils can be assembled into nanotapes via site-specific interactions with pectin

Controlling the self-assembly of individual supramolecular entities, such as amyloid fibrils, into hierarchical architectures enables the 'bottom-up' fabrication of useful bionanomaterials. Here, we present the hierarchical assembly of β-lactoglobulin nanofibrils into the form of 'nanotapes' in the presence of a specific pectin with a high degree of methylesterification. The nanotapes produced were highly ordered, and had an average width of 180 nm at pH 3. Increasing the ionic strength or the pH of the medium led to the disassembly of nanotapes, indicating that electrostatic interactions stabilised the nanotape architecture. Small-angle X-ray scattering experiments conducted on the nanotapes showed that adequate space is available between adjacent nanofibrils to accommodate pectin molecules. To locate the interaction sites on the pectin molecule, it was subjected to endopolygalacturonase digestion, and the resulting products were analysed using capillary electrophoresis and size-exclusion chromatography for their charge and molecular weight, respectively. Results suggested that the functional pectin molecules carry short (<10 residues) enzyme-susceptible blocks of negatively charged, non-methylesterified galacturonic acid residues in the middle of their homogalacturonan backbones (and possibly near their ends), that specifically bind to sites on the nanofibrils. Blocking the interaction sites on the nanofibril surface using small oligomers of non-methylesterified galacturonic acid residues similar in size to the interaction sites of the pectin molecule decreased the nanotape formation, indicating that site-specific electrostatic interactions are vital for the cross-linking of nanofibrils. We propose a structural model for the pectin-cross-linked β-lactoglobulin nanotapes, the elements of which will inform the future design of bionanomaterials.

Structure and Properties of a Non-processive, Salt-requiring, and Acidophilic Pectin Methylesterase from Aspergillus niger Provide Insights into the Key Determinants of Processivity Control

Many pectin methylesterases (PMEs) are expressed in plants to modify plant cell-wall pectins for various physiological roles. These pectins are also attacked by PMEs from phytopathogens and phytophagous insects. The de-methylesterification by PMEs of the O6-methyl ester groups of the homogalacturonan component of pectin, exposing galacturonic acids, can occur processively or non-processively, respectively, describing sequential versus single de-methylesterification events occurring before enzyme-substrate dissociation. The high resolution x-ray structures of a PME from Aspergillus niger in deglycosylated and Asn-linked N-acetylglucosamine-stub forms reveal a 10⅔-turn parallel β-helix (similar to but with less extensive loops than bacterial, plant, and insect PMEs). Capillary electrophoresis shows that this PME is non-processive, halophilic, and acidophilic. Molecular dynamics simulations and electrostatic potential calculations reveal very different behavior and properties compared with processive PMEs. Specifically, uncorrelated rotations are observed about the glycosidic bonds of a partially de-methyl-esterified decasaccharide model substrate, in sharp contrast to the correlated rotations of processive PMEs, and the substrate-binding groove is negatively not positively charged.

Characterization of Gellan Gum by Capillary Electrophoresis

Gellan gums were characterised for the first time using free-solution capillary electrophoresis (CE) or CE under critical conditions (CE-CC). CE-CC is a fast method that separates the polysaccharide. Gellan gums are shown to be heterogeneous in terms of their electrophoretic mobility at 55°C revealing: oligomer peak(s), broad peaks of polymers with a random coil conformation with different degrees of acylation (composition), aggregates, and polymers with double-helix conformation. CE-CC is complementary with the rheological analysis also performed in this work. Sonication of gellan gums is shown to decrease the viscosity of gellan gum mainly by breaking up aggregates. The effect of sonication is stronger on the high-acyl gellan gum since the latter has a far higher tendency to aggregate.

Monoclonal antibodies to rhamnogalacturonan I backbone

Monoclonal antibodies were raised against rhamnogalacturonan I backbone, a pectin domain, using Arabidopsis thaliana seed mucilage-derived rhamnogalacturonan I oligosaccharides--BSA conjugates. Two monoclonal antibodies, designated INRA-RU1 and INRA-RU2, selected for further characterization, were specific for the backbone of rhamnogalacturonan I, displaying no binding activity against the other pectin domains i.e. homogalacturonans, galactans or arabinans. A range of oligosaccharides was prepared by enzymatic digestion of rhamnogalacturonan I isolated from Arabidopsis thaliana seed mucilage and from sugar beet pectin, purified by low-pressure chromatography and characterized by high-performance anion-exchange chromatography and mass spectrometry. These rhamnogalacturonan I oligomers were used to characterize the binding site of the two monoclonal antibodies by competitive inhibition. Both INRA-RU1 and INRA-RU2 showed maximal binding to the [-->2)-alpha-L-rhamnosep-(1-->4)-alpha-D-galacturonic acid p-(1-->](7) structural motif but differed in their minimum binding requirement. INRA-RU2 required at least two disaccharide (rhamnose-galacturonic acid) repeats for the antibody to bind, while INRA-RU1 required a minimum of six disaccharide repeats. Furthermore, the binding capacity of INRA-RU1 decreased steeply as the number of disaccharide repeats go beyond seven. Each of these antibodies reacted with hairy regions isolated from sugar beet pectin. Immunofluorescence microscopy indicated that both antibodies can be readily used to detect rhamnogalacturonan I epitopes in various cell wall samples.