Browsing by Author "Conn, C"

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    Behaviour of single transmembrane peptides during in meso crystallization from the contrast-matched lipidic cubic phase of monoolein
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2018-11-19) van't Hag, L; de Campo, L; Tran, N; Sokolova, AV; Trenker, R; Call, M; Garvey, CJ; Leung., A; Darwish, TA; Krause-Heuer, AM; Knott, RB; Meikle, T; Gras, S; Drummond, CJ; Mezzenga, R; Conn, C
    In meso membrane protein crystallization within a lipidic mesophase has revolutionized the structural biology of integral membrane proteins (IMPs). High-resolution structures of these proteins are crucial to understanding fundamental cellular processes at a molecular level, and can lead to new and improved treatments for a wide range of diseases via rational drug design. However, overall success rates of the promising in meso crystallization technique remain low because of a fundamental lack of understanding about factors that promote crystal growth. In particular, to date, two decades from invention of the method, the protein-eye-view of the in meso crystallization mechanism had not been solved. We have investigated this for the first time using small-angle neutron scattering (SANS). Contrast-matching between the scattering of the lipid membrane formed by MO and the aqueous solution was used to isolate and track the scattering of single-transmembrane peptides during the growth of protein crystals in meso. No peptide enrichment was observed at the flat points of the diamond cubic QIID phase of MO in contrast to suggestions in several modeling studies. During in meso crystallization of the DAP12 peptide a decrease in form factor and a transient fluid lamellar Lα phase could be observed providing direct evidence for the proposed crystallization mechanism. Synthesis of fully deuterated MO was required for this purpose and scattering of this new material in various solvents and under a range of conditions will be described, specifically regarding the effect of the relative scattering length densities (SLD) of the headgroup, acyl chain and solvent, which can advance the use of neutron scattering with other self-assembly materials. © The Authors.
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    Determining the location of encapsulated peptides, proteins, and other biomolecules in contrast-matched lipid bicontinuous cubic phases using SANS
    (International Conference on Neutron Scattering, 2017-07-12) van't Hag, L; de Campo, L; Gras, S; Drummond, CJ; Conn, C
    To evolve biological and biomedical applications of hybrid biomolecule?lipid materials, including in meso protein crystallization and drug delivery, an understanding of the location of the biomolecules within the bicontinuous cubic phases is crucial. Theoretical modeling has indicated that proteins and additive lipids might phase separate locally and adopt a preferred location in the cubic phase, but this has never been experimentally confirmed. We have shown that perfectly contrast-matched cubic phases in D2O can be studied using SANS by mixing fully deuterated and hydrogenated lipid. The model transmembrane peptide WALP21 showed no preferential location in the membrane of the diamond and gyroid cubic phases of phytanoyl monoethanolamide [L. van ‘t Hag et al, J. Phys. Chem. Lett. 2016, 7(14), 2862-2866]. In addition, this result opens up the possibility of studying the conformation (and hence function) of amphiphilic proteins and peptides within a lipid bilayer environment. The effect of deuteration on the cubic phase forming lipid was also investigated to advance the use of neutron scattering techniques to study soft matter systems. Additionally, we have performed extensive characterizations of the cubic phase nanostructure subsequent to protein and peptide incorporation using synchrotron SAXS, as well as the protein and peptide secondary structures using synchrotron circular dichroism spectroscopy [L. van ‘t Hag et al, Langmuir, 2016, 32(27), 6882-6894].
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    Neutron scattering for the study of casein gel microstructure during digestion
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Bayrak, M; Mata, JP; Ranynes, J; Conn, C; Floury, J; Logan, A
    An understanding of the structural factors that affect food digestion kinetics is important for establishing the relationship between their structure and function. To assess the effects of structure on mechanical breakdown and digestibility by pepsin enzyme during gastric digestion, casein gels with an identical composition, but differing by the coagulation mode, were characterized and submitted to simulated in vitro gastric digestion. Rennet-induced (RG) and transglutaminase-induced acid (TG) gels were made and digested in two different solvents - H2O and D2O. The structural changes were assessed during simulated gastric digestion by ultra-small (USANS) and small angle neutron scattering (SANS). The different structures of RG and TG reveal distinctive breakdown behaviours over a hierarchy of length scales (nano- to micro). Different functional properties of casein gels, such as gel strength, elasticity, brittleness, resistance to shear and sensitivity to the acidic environment of gastric phase, obtained by scanning (SEM) and transmission electron microscopy (TEM), contributed to the differences in gel disintegration and gastric digestibility. Despite the higher gel strength and thus higher number of larger gel particles entering the gastric phase following mastication, the porous microstructure of RG provided a larger surface area and thus higher simulated digestibility compared to TG. The effect of acidification is clearer with RG, wherein the local compactness of each gel consequently drives its porosity and pepsin accessibility. On the other hand, pepsin has a limited diffusion capability inside the TG structure due to its fine stranded network; however, the brittle structure of TG is more affected by mechanical shear during the gastric phase, causing particle erosion. In a similar manner, gels made and digested in D2O had a higher level of mechanical breakdown due to their brittle structure: initially led by the fracturing of particles with a larger surface area, this increases the levels of solubilised protein, small peptides and amino acids. Here, we report the first USANS and SANS study to monitor structural changes of a casein gel both in H2O and D2O during simulated in vitro gastric digestion. We show that solvent (H2O and D2O) and gel type (RG and TG) affects digestion components: mechanical shear, enzymatic hydrolysis and the effect of acidification. © The Authors.