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

Abstract

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.

Morphology of complexes formed between β‐lactoglobulin nanofibrils and pectins is influenced by the pH and structural characteristics of the pectins

“…Consequently, the number of β ‐lg nanofibrils cross‐linked by DM86 molecules was lower at pH 2 than at pH 3, resulting in nanotapes with a lower average width. The underlying structure of these extraordinary nanotapes, and the dispersion of the assembly with salt, is elucidated in one of our recent papers.…”

“…Whey protein nanofibrils and pectin have been used to form multilayer microcapsules. The complex formation between β ‐lg nanofibrils and κ ‐carrageenan has been investigated and recently we reported on the interaction of β ‐lg nanofibrils with a specific pectin to form nanotapes.…”

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

“…Homogalacturonan (HG), an extensive linear region of one to four linked galacturonic acid residues, that can each exist in a state of methylesterification or not, is probably the most‐studied domain and is most associated with the mechanical functionality of pectin, both in the cell wall and in its technological applications as a gelling agent. The degree of methylesterification (DM) and the patterning of the methylester groups (and thus charged residues) can be expected to play a key role in determining local polymer mechanics , in controlling the propensity of the chains to self‐assemble into functional networks mediated by ions, hydrogen bonding and hydrophobicity , and in mediating the binding of proteins .…”

Interfacial and emulsifying properties of the electrostatic complex of β-lactoglobulin fibril and gum Arabic (Acacia Seyal)

“…Highly ordered superstructures could be obtained when the electrostatic complex formed by protein aggregates and flexible polysaccharide, [12,13] while an amorphous structures were most likely formed by native protein and flexible polysaccharides. [14] Interestingly, it seems that the ordered structure of protein aggregates/polysaccharide electrostatic complex depends on the charge property and conformation of the polysaccharide.…”

“…[12] In contrast, the electrostatic complexation between BLGF and low molecular weight pectin produced nanotapes. [13] A bottle-brush structure was formed when BLGF interacted with linear and terminal charged polyethylene glycol. [15] In view that BLGF formed electrostatic complexes of various shapes with charged polymers, a wide range of applications of these complexes could be expected.…”