Mechanism of Protein−Poly(ethylene glycol) Interaction from a Diffusive Point of View

Confinements of Thermoresponsive Dendronized Polymers to Proteins

Crowding environment created by host polymers plays crucial roles in manipulating interactions with proteins and modulating their bioactivity. Here, we report our investigation on interactions between polymers and proteins in...

Modulation of enzyme-substrate selectivity using tetraethylene glycol functionalized gold nanoparticles

Tetraethylene glycol (TEG) functionalized gold nanoparticles with 2 nm core diameters (AuTEG) enhance alpha-chymotrypsin (ChT) enzyme activity in a substrate-selective fashion. We explored the hydrolysis of four different substrates and observed a marked increase in activity with the most hydrophobic substrate N-succinyl-alanine-alanine-proline-phenylalanine- p-nitroanilide (TP), while the other substrates remain virtually unaffected by the AuTEG 'crowding effect' in solution. The enhancement in catalysis is indicated by an increase in K(cat)/K(m) as obtained from Lineweaver-Burk analysis and we hypothesize it to arise from a macromolecular crowding effect analogous to that observed with high molecular weight poly(ethylene glycol) (PEG) polymers.

Formation of two-dimensional crystals of icosahedral RNA viruses

The formation of 2D arrays of three small icosahedral RNA viruses with known 3D structures (tomato bushy stunt virus, turnip yellow mosaic virus and bromegrass mosaic virus) has been investigated to determine the role of each component of a negative staining solution containing ammonium molybdate and polyethylene glycol. Virion association was monitored by dynamic light scattering (DLS) and virus array formation was visualised by conventional transmission electron microscopy and cryo-electron microscopy after negative staining. The structural properties of viral arrays prepared in vitro were compared to those of microcrystals found in the leaves of infected plants. A novel form of macroscopic 3D crystals of turnip yellow mosaic virus has been grown in the negative staining solution. On the basis of the experimental results, the hypothesis is advanced that microscopic arrays might be planar crystallisation nuclei. The formation of 2D crystals and the enhancing effect of polyethylene glycol on the self-organisation of virions at the air/water interface are discussed.

SYNOPSIS

The formation of 2D arrays of icosahedral viruses was investigated by spectroscopic and transmission electron microscopic methods.

Effect of Crowding on Protein–Protein Association Rates: Fundamental Differences between Low and High Mass Crowding Agents

Physiological media constitutes a crowded environment that serves as the field of action for protein-protein interaction in vivo. Measuring protein-protein interaction in crowded solutions can mimic this environment. In this work we follow the process of protein-protein association and its rate constants (k(on)) of the beta-lactamase (TEM)-beta-lactamase inhibitor protein (BLIP) complex in crowded solution using both low and high molecular mass crowding agents. In all crowded solutions (0-40% (w/w) of ethylene glycol (EG), poly(ethylene glycol) (PEG) 200, 1000, 3350, 8000 Da Ficoll-70 and Haemaccel the measured absolute k(on), but not k(off) values, were found to be slower as compared to buffer. However, there is a fundamental difference between low and high mass crowding agents. In the presence of low mass crowding agents and Haemaccel k(on) depends inversely on the solution viscosity. In high mass polymer solutions k(on) changes only slightly, even at viscosities 12-fold higher than water. The border between low and high molecular mass polymers is sharp and is dictated by the ratio between the polymer length (L) and its persistence length (Lp). Polymers that are long enough to form a flexible coil (L/Lp > 2) behave as high molecular mass polymers and those who are unable to do so (L/Lp < 2) behave as low molecular mass polymers. We concluded that although polymers solution are crowded, this property is not uniform; i.e. there are areas in the solution that contain bulk water, and in these areas proteins can diffuse and associate almost as if they were in diluted environment. This porous medium may be taken as mimicking some aspects of the cellular environment, where many of the macromolecules are organized along membranes and the cytoskeleton. To determine the contribution of electrostatic attraction between proteins in crowded milieu, we followed k(on) of wt-TEM and three BLIP analogs with up to 100-fold increased values of k(on) due to electrostatic steering. Faster associating BLIP variants keep their relative advantage in all crowded solutions, including Haemaccel. This result suggests that faster associating protein complexes keep their advantage also in complex environment.

Effect of polyethylene glycol on the liquid-liquid phase transition in aqueous protein solutions

We have studied the effect of polyethylene glycol (PEG) on the liquid-liquid phase separation (LLPS) of aqueous solutions of bovine gammaD-crystallin (gammaD), a protein in the eye lens. We observe that the phase separation temperature increases with both PEG concentration and PEG molecular weight. PEG partitioning, which is the difference between the PEG concentration in the two coexisting phases, has been measured experimentally and observed to increase with PEG molecular weight. The measurements of both LLPS temperature and PEG partitioning in the ternary gammaD-PEG-water systems are used to successfully predict the location of the liquid-liquid phase boundary of the binary gammaD-water system. We show that our LLPS measurements can be also used to estimate the protein solubility as a function of the concentration of crystallizing agents. Moreover, the slope of the tie-lines and the dependence of LLPS temperature on polymer concentration provide a powerful and sensitive check of the validity of excluded volume models. Finally, we show that the increase of the LLPS temperature with PEG concentration is due to attractive protein-protein interactions.