Examining the inorganic elemental composition of lobster phyllosoma (Panulirus ornatus) with X-ray fluorescence microscopy.

The ornate spiny rock lobster, Panulirus ornatus, is an attractive candidate for aquaculture. The larval stages of spiny lobsters, known as phyllosoma, are complex with many developmental stages. Very little is known about the inorganic element composition of phyllosoma. In this study, a novel method using synchrotron X-ray fluorescence microscopy (XFM) was applied to investigate the distributions of metals potassium (K), calcium (Ca), copper (Cu), zinc (Zn), the metalloid arsenic (As), and nonmetal bromine (Br) within individual phyllosoma at stages 3, 4, and 8 of their development. For the first time, 1 µm resolution synchrotron XFM images of whole phyllosoma as well as closer examinations of their eyes, mouths, setae, and tails were obtained. Elements accumulated in certain locations within phyllosoma, providing insight into their likely biological role for these organisms. This information may be useful for the application of dietary supplementation in the future to closed larval cycle lobster aquaculture operations.

The Assembly Mechanism and Mesoscale Architecture of Protein-Polysaccharide Complexes Formed at the Solid-liquid Interface.

Protein-polysaccharide composite materials have generated much interest due to their potential use in medical science and biotechnology. A comprehensive understanding of the assembly mechanism and the mesoscale architecture is needed for fabricating protein-polysaccharide composite materials with desired properties. In this study, complex assemblies were built on silica surfaces through a layer-by-layer (LbL) approach using bovine beta-lactoglobulin variant A (ßLgA) and pectin as model protein and polysaccharide, respectively. We demonstrated the combined use of quartz crystal microbalance with dissipation monitoring (QCM-D) and neutron reflectometry (NR) for elucidating the assembly mechanism as well as the internal architecture of the protein-polysaccharide complexes formed at the solid-liquid interface. Our results show that ßLgA and pectin interacted with each other and formed a cohesive matrix structure at the interface consisting of intertwined pectin chains that were cross-linked by ßLgA-rich domains. Although the complexes were fabricated in an LbL fashion, the complexes appeared to be relatively homogeneous with ßLgA and pectin molecules spatially distributed within the matrix structure. Our results also demonstrate that the density of ßLgA-pectin complex assemblies increased with both the overall and local charge density of pectin molecules. Therefore, the physical properties of the protein-polysaccharide matrix structure, including density and level of hydration, can be tuned by using polysaccharides with varying charge patterns, thus promoting the development of composite materials with desired properties.

Locking the Spiro Carbon in Spirobisindane Using Sulfur and Phosphorus to Form "Olympic Ring"-like Molecules.

To improve the rigidity of spirobisindane, it was intramolecularly locked by forming eight-membered rings via sulfur and phosphorus atoms to produce an interlocked polycyclic structure under mild conditions in good yields. By carefully analyzing the crystal structures, we noticed that the angle between the two benzene rings in the locked version is significantly smaller than that of the typical spirobisindane structure. Molecular modeling indicated that locking the spiro center can remarkably enhance the rigidity.

Morphology of complexes formed between ß-lactoglobulin nanofibrils and pectins is influenced by the pH and structural characteristics of the pectins.

For the optimal use of ß-lactoglobulin nanofibrils as a raw material in biological composites an in-depth knowledge of their interactions with other constituents is necessary. To understand the effect of electrostatic interactions on the morphology of resulting complexes, ß-lactoglobulin nanofibrils were allowed to interact with pectins in which the amount of available negative charge was controlled by selecting their degree of methylesterification. In this study, citrus pectins having different degrees of methylesterification (∼48, 67, 86, and 97%) were selected and interacted with nanofibrils at pH 2 and pH 3, where they possess a net positive charge. Electrostatic complexes formed between ß-lactoglobulin nanofibrils and all pectin types, except for the sample having a degree of methylesterification of 97%. The morphology of these complexes, however, differed significantly with the degree of methylesterification of the pectin, its concentration, and the pH of the medium, revealing that distinct desired biological architectures can be attained relatively easily through manipulating the electrostatic interactions. Interestingly, the pectin with a degree of methylesterification of 86% was found to crosslink the ß-lactoglobulin nanofibrils into ordered 'nanotapes'.

ß-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 ß-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 ß-lactoglobulin nanotapes, the elements of which will inform the future design of bionanomaterials.

Structural mechanism of complex assemblies: characterisation of beta-lactoglobulin and pectin interactions.

Knowledge of how proteins and polysaccharides interact is the key to understanding encapsulation and emulsification in these composite systems and ultimately to understanding the structures of many biological network systems. As a model system we have studied ß-lactoglobulin A (ßLgA) interacting with pectins of various amounts and distribution patterns of charge. The studies were conducted at pH 4 at minimal ionic strength, where the ßLgA and the pectins are oppositely charged, resulting in an electrostatic attraction to each other. Isothermal titration calorimetry (ITC) experiments were performed to determine the thermodynamics associated with ßLgA-pectin titration. It was found that ßLgA only interacted with pectins with an adequate amount of charge, and that the complexation between ßLgA and pectin was a two-step process initially involving binding of the protein to available sites on the pectin, and subsequently binding of the protein onto the bound protein that has previously adsorbed. Circular dichroism (CD) and intrinsic tryptophan fluorescence were also measured of ßLgA during its interaction with the pectin samples, and show that the binding leads to significant conformational changes in ßLgA. An increase in the turbidity of the solution of the resultant complexes indicates the formation of large-scale interpolymer associations of the primary complexes mediated by protein-rich domains.