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

Xu, Amy Y.; Melton, Laurence D.; Jameson, Geoffrey B.; Williams, Martin A. K.; McGillivray, Duncan J.

doi:10.1039/c5sm01378j

Cited by 66 publications

(21 citation statements)

References 62 publications

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“…Even sharing the hydration shell between proteins in a crowded solution alone will increase the net entropy of the total system’s solvent, if the protein concentration within the coacervation is very high and the protein preserves its dynamics and hydration shell as in dilute solution state. Notably, there are several reports in the literature on the spontaneous complex coacervation of synthetic polyelectrolyte and protein (e.g., β-lactoglobulin) constituents to be entropy-driven [6, 18, 24, 45, 46], but no studies combine macroscopic thermodynamic measurements with studies of local protein dynamics and conformations. We show that the majority of tau complexed with RNA in the highly condensed droplet state maintains locally the dynamical conformations of free tau as populated in dilute solution state.…”

Section: Discussionmentioning

confidence: 99%

RNA stores tau reversibly in complex coacervates

et al. 2017

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Nonmembrane-bound organelles that behave like liquid droplets are widespread among eukaryotic cells. Their dysregulation appears to be a critical step in several neurodegenerative conditions. Here, we report that tau protein, the primary constituent of Alzheimer neurofibrillary tangles, can form liquid droplets and therefore has the necessary biophysical properties to undergo liquid-liquid phase separation (LLPS) in cells. Consonant with the factors that induce LLPS, tau is an intrinsically disordered protein that complexes with RNA to form droplets. Uniquely, the pool of RNAs to which tau binds in living cells are tRNAs. This phase state of tau is held in an approximately 1:1 charge balance across the protein and the nucleic acid constituents, and can thus be maximal at different RNA:tau mass ratios, depending on the biopolymer constituents involved. This feature is characteristic of complex coacervation. We furthermore show that the LLPS process is directly and sensitively tuned by salt concentration and temperature, implying it is modulated by both electrostatic interactions between the involved protein and nucleic acid constituents, as well as net changes in entropy. Despite the high protein concentration within the complex coacervate phase, tau is locally freely tumbling and capable of diffusing through the droplet interior. In fact, tau in the condensed phase state does not reveal any immediate changes in local protein packing, local conformations and local protein dynamics from that of tau in the dilute solution state. In contrast, the population of aggregation-prone tau as induced by the complexation with heparin is accompanied by large changes in local tau conformations and irreversible aggregation. However, prolonged residency within the droplet state eventually results in the emergence of detectable β-sheet structures according to thioflavin-T assay. These findings suggest that the droplet state can incubate tau and predispose the protein toward the formation of insoluble fibrils.

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Section: Discussionmentioning

confidence: 99%

RNA stores tau reversibly in complex coacervates

et al. 2017

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“…Notably, there are several reports in the literature on the spontaneous complex coacervation of synthetic polyelectrolyte and protein (e.g. β-lactoglobulin) constituents to be entropy-driven [6,18,24,45,46], but no studies combine macroscopic thermodynamic measurements with studies of local protein dynamics and conformations. We show that the majority of tau complexed with RNA in the highly condensed Linking the in vitro observations of tau-RNA coacervation to in vivo structures that share many of the properties we describe here remains a challenge for the field.…”

Section: Discussionmentioning

confidence: 99%

RNA Stores Tau Reversibly in Complex Coacervates

Zhang

Lin

Eschmann

et al. 2017

Preprint

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Non-membrane-bound organelles that behave like liquid droplets are widespread among eukaryotic cells. Their dysregulation appears to be a critical step in several neurodegenerative conditions. Here we report that tau protein, the primary constituent of Alzheimer neurofibrillary tangles, can form liquid droplets and therefore has the necessary biophysical properties to undergo liquid-liquid phase separation (LLPS) in cells. Consonant with the factors that induce LLPS, tau is an intrinsically disordered protein that complexes with RNA to form droplets. Uniquely, the pool of RNAs to which tau binds in living cells are tRNAs. This phase state of tau is held in an approximately 1:1 charge balance across the protein and the nucleic acid constituents, and can thus be maximal at different RNA:tau mass ratios depending on the biopolymer constituents involved. This feature is characteristic of complex coacervation. We furthermore show that the LLPS process is directly and sensitively tuned by salt concentration and temperature, implying it is modulated by both electrostatic interactions between the involved protein and nucleic acid constituents, as well as net changes in entropy. Despite the high protein concentration within the complex coacervate phase, tau is locally freely tumbling and capable of diffusing through the droplet interior. In fact, tau in the condensed phase state does not reveal any immediate changes in local protein packing, local conformations and local protein dynamics from that of tau in the dilute solution state. In contrast, the population of aggregation-prone tau as induced by the complexation with heparin is accompanied by large changes in local tau conformations and irreversible aggregation. However, prolonged residency within the droplet state eventually results in the emergence of detectable β-sheet structures according to thioflavin-T assay. These findings suggest that the droplet state can incubate tau and pre-dispose the protein toward the formation of insoluble fibrils.

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“…Decreasing the pH value of the solution to 3.5, in the UM7 method, is accompanied by an increase in positive charge on the surface of the protein molecules and a decrease in negative charge of the pectin molecules leading to a lower net negative charge on the complex. Consequently, the electrostatic repulsion reduces and polymer bridges are formed between protein molecules and a shared pectin molecule (Jones et al., 2010b; Xu et al., 2015).…”

Section: Resultsmentioning

confidence: 99%

“…Pectin molecules have long galacturonic regions (smooth regions) and side chains (hairy regions) and are characterized by sugars, such as rhamnose, galactose, and arabinose, attached to the pectin backbone. Although pectin–WPI complexes have been extensively investigated, SSPS–WPI complexes are rarely studied (Girard, Turgeon, & Gauthier, 2003; Jensen et al., 2010; Jones et al., 2010a, 2010b; Krzeminski et al., 2014; Protte, Balinger, Weiss, Löffler, & Nöbel, 2018; Wagoner, & Foegeding, 2017; Xu, Melton, Jameson, Williams, & McGillivray, 2015).…”

Section: Introductionmentioning

confidence: 99%

Exceptional colloidal stability of acidified whey protein beverages stabilized by soybean soluble polysaccharide

Zamani

Zhang

et al. 2020

Journal of Food Science

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Protein-rich beverages have gained significant attention in recent years. It is a challenge to produce whey protein beverages with high stability, good transparency, and a smooth mouthfeel. The polysaccharide (PS)-protein complex might help the food industry overcome these obstacles. In this study, soybean soluble polysaccharide (SSPS) and high methoxylated pectin (HMP, a traditional PS) are used, at different ratios to the protein, to improve the colloidal stability of the acidified whey protein solution. Both heated and unheated complexes were studied. SSPS-whey protein complexes have shown exceptional stabilities in all ratios while HMP-whey protein complexes revealed coacervation after 72 hr of storage. The prepared complexes exhibited comparable sizes and ζ -potentials. The SSPS-whey protein complexes were less turbid than HMP-whey protein complexes at similar PS to protein ratios. Results also show that greater repulsive interactions occurred in SSPS-whey protein complexes when compared to HMP-whey protein complexes, as examined by free thiol content and intrinsic fluorescence intensity measurements.Practical Application: It is a challenge to produce whey protein isolate (WPI) beverages with high stability, good transparency, and smooth mouthfeel. The polysaccharide (PS)-protein complex might help the food industry overcome these obstacles. We have demonstrated that soybean soluble polysaccharide (SSPS), at [SSPS]:[acWPI] ratios of 1:2 to 1:30, can significantly improve the colloidal stability of the acidified whey protein beverages. This SSPS-whey protein system could be used as a stable beverage base for a variety of beverages.

show abstract

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

Cited by 66 publications

References 62 publications

RNA stores tau reversibly in complex coacervates

RNA stores tau reversibly in complex coacervates

RNA Stores Tau Reversibly in Complex Coacervates

Exceptional colloidal stability of acidified whey protein beverages stabilized by soybean soluble polysaccharide

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