The physics of protein self-assembly

Strategies and perspectives of assembling multi-enzyme systems

Multi-enzyme complexes have the potential to achieve high catalytic efficiency for sequence reactions due to their advantages in eliminating product inhibition, facilitating intermediate transfer and in situ regenerating cofactors. Constructing functional multi-enzyme systems to mimic natural multi-enzyme complexes is of great interest for multi-enzymatic biosynthesis and cell-free synthetic biotransformation, but with many challenges. Currently, various assembly strategies have been developed based on the interaction of biomacromolecules such as DNA, peptide and scaffolding protein. On the other hand, chemical-induced assembly is based on the affinity of enzymes with small molecules including inhibitors, cofactors and metal ions has the advantage of simplicity, site-to-site oriented structure control and economy. This review summarizes advances and progresses employing these strategies. Furthermore, challenges and perspectives in designing multi-enzyme systems are highlighted.

DNA-modified artificial viral capsids self-assembled from DNA-conjugated β-annulus peptide

β-Annulus peptides from tomato bushy stunt virus conjugated with DNAs (dA₂₀ and dT₂₀ ) at the C-terminal were synthesized. The DNA-modified β-annulus peptides self-assembled into artificial viral capsids with sizes of 45-160 nm. ζ-Potential measurements revealed that the DNAs were coated on the surface of artificial viral capsids. Fluorescence assays indicated that the DNAs on the artificial viral capsids were partially hybridized with the complementary DNAs. Moreover, the DNA-modified artificial viral capsids formed aggregates by adding complementary polynucleotides. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

Protein self-assembly following in situ expression in artificial and mammalian cells

The importance of in vitro measurements in explaining the mechanisms underlying protein self-assembly in physiologically relevant conditions has been demonstrated in solution and in artificial and mammalian cells.

Heteroprotein complex coacervation: A generic process

Proteins exhibit a rich diversity of functional, physico-chemical and biodegradable properties which makes them appealing for various applications in the food and non-food sectors. Such properties are attributed to their ability to interact and assemble into a diversity of supramolecular structures. The present review addresses the updated research progress in the recent field of complex coacervation made from mixtures of oppositely charged proteins (i.e. heteroprotein systems). First, we describe briefly the main proteins used for heteroprotein coacervation. Then, through some selected examples, we illustrate the particularity and specificity of each heteroprotein system and the requirements that drive optimal assembly into coacervates. Finally, possible and promising applications of heteroprotein coacervates are mentioned.

Limiting the valence: advancements and new perspectives on patchy colloids, soft functionalized nanoparticles and biomolecules

Artistic representation of limited valance units consisting of a soft core (in blue) and a small number of flexible bonding patches (in orange).

Strings and stripes formed by a protein system interacting via a single-patch attraction

The phase behavior of lactoferrin has been studied as a function of concentration at a pH and ionic strength where lactoferrin is known to interact effectively via a patch-patch attraction. In contrast to isotropic attractive potentials, the directional attraction gives rise to a different phase or solution behavior. At low concentrations, the protein dimerizes. As the concentration is increased, the protein self-assembles into elongated, stripe-like structures at intermediate protein concentrations, a behavior which has been predicted for the case of attractive one-patch colloids. The stripe phase is surprisingly difficult to detect using conventional techniques, i.e. small-angle X-ray scattering, since only a small fraction of the proteins participate in the stripes combined with sedimentation due to micron-sized entities. This is circumvented by monitoring the change in the overall protein concentration by static light scattering and the stripe formation can be followed. For visualization of the structures cryo-TEM is used.

Modeling phase transitions in mixtures of β-γ lens crystallins

We analyze the experimentally determined phase diagram of a γD-βB1 crystallin mixture. Proteins are described as dumbbells decorated with attractive sites to allow inter-particle interaction. We use thermodynamic perturbation theory to calculate the free energy of such mixtures and, by applying equilibrium conditions, also the compositions and concentrations of the co-existing phases. Initially we fit the Tcloudversus packing fraction η measurements for a pure (x2 = 0) γD solution in 0.1 M phosphate buffer at pH = 7.0. Another piece of experimental data, used to fix the model parameters, is the isotherm x2vs. η at T = 268.5 K, at the same pH and salt content. We use the conventional Lorentz-Berthelot mixing rules to describe cross interactions. This enables us to determine: (i) model parameters for pure βB1 crystallin protein and to calculate; (ii) complete equilibrium surface (Tcloud-x2-η) for the crystallin mixtures. (iii) We present the results for several isotherms, including the tie-lines, as also the temperature-packing fraction curves. Good agreement with the available experimental data is obtained. An interesting result of these calculations is evidence of the coexistence of three phases. This domain appears for the region of temperatures just out of the experimental range studied so far. The input parameters, leading good description of experimental data, revealed a large difference between the numbers of the attractive sites for γD and βB1 proteins. This interesting result may be related to the fact that γD has a more than nine times smaller quadrupole moment than its partner in the mixture.

Tripeptide consisting of benzyl protected di-cysteine and phenylalanine forms spherical assembly and induces cytotoxicity in cancer cells via apoptosis

Tripeptide self assemblies in cell growth medium induce apoptosis and promoting cancer cell death at submicromolar concentration.