Biomolecular condensation of the microtubule-associated protein tau.

Cells contain multiple compartments dedicated to the regulation and control of biochemical reactions. Cellular compartments that are not surrounded by membranes can rapidly form and dissolve in response to changes in the cellular environment. The physicochemical processes that underlie the formation of non-membrane-bound compartments in vivo are connected to liquid-liquid phase separation of proteins and nucleic acids in vitro. Recent evidence suggests that the protein tau, which plays an important role in Alzheimer's disease and other neurodegenerative disorders, phase separates in solution, forms tau phases with microtubules, and associates with phase-separated RNA-binding protein granules in cells. Here we review the experimental evidence that supports the ability of tau to phase separate in solution and form biomolecular condensates in cells. As for other disease-relevant proteins, the physiological and pathological functions of tau are tightly connected - through loss of normal function or gain of toxic function - and we therefore discuss how tau phase separation plays a role for both, and with respect to different cellular functions of tau

Interactions of the potent synthetic AT1 antagonist analog BV6 with membrane bilayers and mesoporous silicate matrices

The present work describes the drug:membrane interactions and a drug delivery system of the novel potent AT1 blocker BV6. This designed analog has most of the pharmacological segments of losartan and an additional biphenyltetrazole moiety resulting in increased lipophilicity. We found that BV6:membrane interactions lead to compact bilayers that may in part explain its higher in vitro activity compared to losartan since such environment may facilitate its approach to AT1 receptor. Its high docking score to AT1 receptor stems from more hydrophobic interactions compared to losartan. X-ray powder diffraction (XRPD) and thermogravimetric analysis (TGA) have shown that BV6 has a crystalline form that is not decomposed completely up to 600 °C. These properties are desirable for a drug molecule. BV6 can also be incorporated into a mesoporous silicate drug-delivery matrix SBA-15. The properties of the obtained drug-delivery system have been inspected by XRD, 13C CP/MAS, TGA and nitrogen sorption experiments

Lysine/RNA-interactions drive and regulate biomolecular condensation.

Cells form and use biomolecular condensates to execute biochemical reactions. The molecular properties of non-membrane-bound condensates are directly connected to the amino acid content of disordered protein regions. Lysine plays an important role in cellular function, but little is known about its role in biomolecular condensation. Here we show that protein disorder is abundant in protein/RNA granules and lysine is enriched in disordered regions of proteins in P-bodies compared to the entire human disordered proteome. Lysine-rich polypeptides phase separate into lysine/RNA-coacervates that are more dynamic and differ at the molecular level from arginine/RNA-coacervates. Consistent with the ability of lysine to drive phase separation, lysine-rich variants of the Alzheimer's disease-linked protein tau undergo coacervation with RNA in vitro and bind to stress granules in cells. Acetylation of lysine reverses liquid-liquid phase separation and reduces colocalization of tau with stress granules. Our study establishes lysine as an important regulator of cellular condensation

Challenges and approaches to understand cholesterol-binding impact on membrane protein function: An NMR view.

Experimental evidence for a direct role of lipids in determining the structure, dynamics, and function of membrane proteins leads to the term 'functional lipids'. In particular, the sterol molecule cholesterol modulates the activity of many membrane proteins. The precise nature of cholesterol-binding sites and the consequences of modulation of local membrane micro-viscosity by cholesterol, however, is often unknown. Here, we review the current knowledge of the interaction of cholesterol with transmembrane proteins, with a special focus on structural aspects of the interaction derived from nuclear magnetic resonance approaches. We highlight examples of the importance of cholesterol modulation of membrane protein function, discuss the specificity of cholesterol binding, and review the proposed binding motifs from a molecular perspective. We conclude with a short perspective on what could be future trends in research efforts targeted towards a better understanding of cholesterol/membrane protein interactions

Challenges and approaches to understand cholesterol-binding impact on membrane protein function: An NMR view.

Experimental evidence for a direct role of lipids in determining the structure, dynamics, and function of membrane proteins leads to the term 'functional lipids'. In particular, the sterol molecule cholesterol modulates the activity of many membrane proteins. The precise nature of cholesterol-binding sites and the consequences of modulation of local membrane micro-viscosity by cholesterol, however, is often unknown. Here, we review the current knowledge of the interaction of cholesterol with transmembrane proteins, with a special focus on structural aspects of the interaction derived from nuclear magnetic resonance approaches. We highlight examples of the importance of cholesterol modulation of membrane protein function, discuss the specificity of cholesterol binding, and review the proposed binding motifs from a molecular perspective. We conclude with a short perspective on what could be future trends in research efforts targeted towards a better understanding of cholesterol/membrane protein interactions

Inversion of pore size dependence of solute transport kinetics from increasingly attractive ordered porous matrix.

The problem of solute transport in interacting ordered porous media is addressed by numerically solving the 2D Fokker-Planck equation using 4-step operator splitting. The subtle interplay between drift and diffusion is shown to result in a nontrivial dependence of solute transport kinetics on pore size. Depending on the strength of attraction to pore walls distinct regimes of pore size dependence of transport kinetics are found. The results suggest a decoupling of local dynamics from large-scale transport

Modus operandi of controlled release from mesoporous matrices: A theoretical perspective.

The ability to alter the rate at which molecules are released from pores by manipulating structural and surface properties of mesoporous materials was demonstrated consistently in numerous studies. Yet an understanding of the role of pore size, attraction to pore walls and of the release mechanism in general has still been elusive. Here we address these issues by means of a simple 2-dimensional (2D) model of ordered porous matrices with various pore sizes and strengths of molecule-wall attractions. The system dynamics are described with a 2D Fokker-Planck equation which is solved numerically for various cases of initial concentration distribution. We show that the interactions with walls play an essential and fundamental role in controlled release from mesoporous materials, regardless of whether they are additionally functionalized or not. They affect the relative cross-section where the local flux has a non-vanishing axial component and accordingly the effective transfer rate into bulk solution. Furthermore the inclusion of molecule-wall attractions into the theoretical description turns out to be the missing piece of the puzzle that explains the origin of the experimentally observed dependence of release kinetics on the pore size. Our results enable us to reinterpret existing experimental findings and provide a revised view of the mechanism of controlled release from ordered porous matrices

The giant keyhole limpet radular teeth A naturally grown harvest machine

AbstractThe limpet radula is a feeding organ, which contains more than 100 rows of teeth. During their growth the teeth mature and advance in position along the radula. The simpler doccoglossan radulae operate by grinding rocky substrates, extracting the algae by rasping and scraping with the teeth functioning as shovels. Less is known about the rhipidoglossan radulae, used as rakes or brooms that brush and collect loose marine debris. This type of radula is found in the giant keyhole limpet (Megathura crenulata). The large size of this organism suggests that the rhipidoglossan radula entails a technological superiority for M. crenulata in its habitat. The structure and function of the radulae teeth have however not been reported in detail. Using a combination of 2D and 3D microscopy techniques coupled with amino acid analysis and X-ray scattering, we reveal the working components of M. crenulata’s radula. It is characterized by numerous marginal teeth surrounding a pair of major hook-like lateral teeth, two pairs of minor lateral teeth and a large central tooth. The mature major lateral teeth show pronounced signs of wear, which gradually increase towards the very front end of the radula and are evidence for scraping. An abrupt change in the amino acid composition in the major lateral teeth and the concurrent formation of a chitinous fiber-network mark the onset of tooth maturation. In comparison to the simpler rock-scraping doccoglossate limpets, the radula of M. crenulata forms an elaborate feeding apparatus, which can be seen as a natural harvest machine

Understanding controlled drug release from mesoporous silicates: Theory and experiment.

Based on the results of carefully designed experiments upgraded with appropriate theoretical modeling, we present clear evidence that the release curves from mesoporous materials are significantly affected by drug-matrix interactions. In experimental curves, these interactions are manifested as a non-convergence at long times and an inverse dependence of release kinetics on pore size. Neither of these phenomena is expected in non-interacting systems. Although both phenomena have, rather sporadically, been observed in previous research, they have not been explained in terms of a general and consistent theoretical model. The concept is demonstrated on a model drug indomethacin embedded into SBA-15 and MCM-41 porous silicates. The experimental release curves agree exceptionally well with theoretical predictions in the case of significant drug-wall attractions. The latter are described using a 2D Fokker-Planck equation. One could say that the interactions affect the relative cross-section of pores where the local flux has a non-vanishing axial component and in turn control the effective transfer of drug into bulk solution. Finally, we identify the critical parameters determining the pore size dependence of release kinetics and construct a dynamic phase diagram of the various resulting transport regimes