Liquid–Liquid Phase Separation of the Green Mussel Adhesive Protein Pvfp‐5 is Regulated by the Post‐Translated Dopa Amino Acid
Kanagavel DeepankumarQi GuoHarini MohanramJessica LimYuguang MuKonstantin PervushinJing YuAli Miserez
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Abstract:
The underwater adhesive prowess of aquatic mussels has been largely attributed to the abundant post-translationally modified amino acid l-3,4-dihydroxyphenylalanine (Dopa) in mussel foot proteins (MFPs) that make up their adhesive threads. More recently, it has been suggested that during thread fabrication, MFPs form intermediate fluidic phases such as liquid crystals or coacervates regulated by a liquid-liquid phase separation (LLPS) process. Here, it is shown that Dopa plays another central role during mussel fiber formation, by enabling LLPS of Pvfp-5β, a main MFP of the green mussel Perna viridis. Using residue-specific substitution of Tyrosine (Tyr) for Dopa during recombinant expression, Dopa-substituted Pvfp-5β is shown to exhibit LLPS under seawater-like conditions, whereas the Tyr-only version forms insoluble aggregates. Combining quantum chemistry calculations and solution NMR, a transient H-bonding network requiring the two hydroxyl groups of Dopa is found to be critical to enable LLPS in Dopa-mutated Pvfp-5β. Overall, the study suggests that Dopa plays an important role in regulating LLPS of MFPs, which may be critical to concentrate the adhesive proteins at the plaque/substrate interface and therefore produce a more robust adhesive. The findings also provide molecular-level lessons to guide biomanufacturing of protein-based materials such as bioadhesives and load-bearing fibers.Keywords:
Coacervate
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A gelatin and sodium alginate complex coacervation system was studied and an effect of pH and colloid mixing ratios on coacervation was investigated. A colloid mixing ratio at which optimum coacervation occurred varied with the coacervation pH. Viscometric, turbidity and coacervate dry yield investigations were used to investigate optimum conditions for complex coacervation. Optimum coacervation occurred at pH 3.5 at a gelatin sodium alginate ratio 4:1. Coacervate and equilibrium fluid was analyzed for gelatin and sodium alginate contents and yields calculated on the basis of chemical analysis showed that optimum coacervation occurred at 25% sodium alginate fraction at pH 3.5.
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Gelatin
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The coacervation of polyphosphates usually takes place at very low pH value. We show that, in the system Na2O-CaO - P2O5, the decrease of pH is due the hydrolysis of the terminal P-OH groups and that it is a consequence of the coacervation. So a very low pH is not necessary to obtain a coacervate and it is possible to form coacervates in non-acid media (even basic). The same results are obtained with other precursor systems of polyphosphate coacervates. These results may be interesting for the achievement of coacervates as industrial glasses precursors.
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Adhesives are crucial both in nature and in diversified artificial fields, and developing environment-friendly adhesives with economic procedures remains a great challenge. We report that folic acid-based coacervates can be a new category of excellent adhesives for all kinds of surfaces with long-lasting adhesiveness. Aided by the electrostatic interaction between the π–π stacked folic acid quartets and polycations, the resultant coacervates are able to interact with diversified substrates via a polyvalent hydrogen bond, coordination, and electrostatic interactions. The adhesivity to wood is superior to the strong commercial glues, but without releasing any toxic components. Upon evaporating water, the coacervate can be casted into a non-adhesive flexible self-supporting film, which restores the adhesive coacervate immediately on contacting water with original adhesive ability. In this way, the coacervate can be facilely tailored into a double-sided tape (DST), which is convenient for storage and application under ambient conditions. Given its excellent adhesive performance, release of nontoxic gases, and convenience in storage and application, the folic acid-based DST is very promising as a new adhesive material.
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Self-coacervation of animal-derived proteins has been extensively investigated while that of plant proteins remains largely unexplored. Here, we study the process of soy glycinin self-coacervation and transformation into hollow condensates. The protein hexameric structure composed of hydrophilic and hydrophobic polypeptides is crucial for coacervation. The process is driven by charge screening of the intrinsically disordered region of acidic polypeptides, allowing for weak hydrophobic interactions between exposed hydrophobic polypeptides. We find that the coacervate surface exhibits order, which stabilizes the coacervate shape during hollow-condensate formation. The latter process occurs via nucleation and growth of protein-poor phase in the coacervate interior, during which another ordered layer at the inner surface is formed. Aging enhances the stability of both coacervates and hollow condensates. Understanding plant protein coacervation holds promises for fabricating novel functional materials.
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Single stranded DNA (ssDNA), or another polyanion, can be mixed with polycations to form liquid-like complex coacervates. When the polycations are replaced by cationic-neutral diblock copolymers, complex coacervate core micelles (C3Ms) can be formed instead. In both complex coacervates and C3Ms, dynamics plays an important role. Yet, to date, the effect of chain length on the dynamics effect is still not fully understood. The DNA complexes provide a versatile platform to further elucidate these chain length effects because the DNA is monodisperse and its length can be easily adapted. Therefore, we study in this paper the dynamics of fluorescently labelled ssDNA in both complex coacervate droplets and micelles. The DNA dynamics in the complex coacervate droplets is probed by fluorescence recovery after photobleaching (FRAP). We observe that the DNA diffusion coefficient depends more strongly on the DNA length than predicted by the sticky Rouse model and we show that this can be partly explained by changes in complex coacervate density, but that also other factors might play a role. We measure the molecular exchange of C3Ms by making use of Förster resonance energy transfer (FRET) and complement these measurements with Langevin dynamics simulations. We conclude that chain length polydispersity is the main cause of a broad distribution of exchange rates. We hypothesise that the different exchange rates that we observe for the monodisperse DNA are mainly caused by differences in dye interactions and show that the dye can indeed have a large effect on the C3M exchange. In addition, we show that a new description of the C3M molecular exchange is required that accounts among others for the effect of the length of the oppositely charged core species. Together our findings can help to better understand the dynamics in both specific DNA systems and in complex coacervate droplets and micelles in general.
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Coacervates have been extensively investigated for their possible role as protocells in the origin of life on earth. Early work in this area has been reviewed by Yevreinova (1). Other research on coacervation has centered around microencapsulation of substances to isolate or selectively release them for industrial applications (2-10). The purpose of this paper is to review the formation of coacervate systems and the characteristics and alterations of those characteristics of coacervates, and to discuss the results of our investigations of coacervates as models for plant tissue cells. Much of the background material discussed in this paper is based on the excellent review of coacervates by Yevreinova (1). Homogeneous, transparent solutions of proteins, carbohydrates, and other compounds can separate into two layers, one depleted and one enriched with these compounds. The process of separation of macromolecules into discrete entities is termed coacervation. The layer rich in molecules of the dissolved
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Protocell
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Abstract Phase boundary determination, coacervate volume measurements and analysis of the phases have been made to assess the influence of pH on the coacervation of gelatin solutions by ethanol and sodium sulphate. Coacervation was found to be pH dependent. In the ethanol system coacervation was noticeable only within a pH range in the vicinity of the isoionic point; at other pH values either a viscous gel phase or floccules occurred. In the sodium sulphate system, coacervation occurred at all pH values examined. The effect of pH in changing the overall charge on the gelatin molecule is explained in relation to the formation of gelatin coacervates. Finally, the role of the coacervate phase in the microencapsulation of oil and solid particulates is discussed.
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Gelatin
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