Controlling Protein Assembly with Superchaotropic Nano-Ions

Analytical ultracentrifugation as a tool for exploring COSAN assemblies

The self-assembly of the cobaltabis(dicarbollide) (COSAN) anionic boron clusters into micelles above a critical micelle concentration (cmc) of 10-20 mM and its behavior as "sticky nano-ions" facilitating controlled protein aggregation have been previously investigated using scattering techniques. These techniques effectively provide average structural parameters but, when applied to colloidal systems, often rely on models assuming polydispersity or anisotropic shapes. Here, we employed sedimentation velocity analytical ultracentrifugation (SV-AUC), which offers the ability to resolve discrete species. We revisited two key questions: (1) the aggregation behavior of COSAN into micelles, a topic still under debate, and (2) the nature of the protein assemblies induced by COSAN, specifically their size/shape distribution and aggregation number. SV-AUC confirms the cmc of COSAN of 16 mM and reveals that COSAN micelles exhibit low aggregation numbers (8 in water and 14 in dilute salt), consistent with recent hypotheses. It shows that COSAN promotes myoglobin aggregation into discrete oligomeric species with well-defined aggregation numbers, such as dimers, tetramers, and higher-order assemblies, depending on the COSAN-to-protein ratio. COSAN binding could be quantified at the lower COSAN/myoglobin ratios. For example, at ratio 5, myoglobin monomer (25%) binds about two COSANs, dimer (45%) about 14 COSANs, and there are ≈ 30% very large aggregates. These results provide clarity on the discrete nature of COSAN micelle aggregation and protein assembly. This study highlights the complementary role of SV-AUC in understanding supramolecular assemblies, offering useful insights into the behavior of COSAN nano-ions and their interactions with biomacromolecules.

Design of Multimodal Supramolecular Protein Assemblies via Enzyme-Substrate Interactions for Intracellular Antioxidant Regulation

Allosteric modulation of protein function, which involves effector binding triggering distant conformational changes, is crucial for cellular and metabolic control. However, achieving tunable control, structural diversity, and precise intracellular regulation remains challenging. Here, we designed dynamic supramolecular protein assemblies driven by enzyme-substrate interactions for antioxidant regulation in cells. Using a glutathione S-transferase modified with a cysteine mutation (GSTK77C), we engineered an effector molecule (GMP4M) containing a glutathione (GSH) moiety and maleimide group linked by a PEG chain. This system forms hierarchical protein assemblies with diverse morphologies, including nanowires, nanorings, nanobranches, and nanotwists, and switchable "ON/OFF" enzymatic activity modulated by endogenous GSH. The assemblies maintain structural integrity under physiological conditions, show remarkable reversibility, and outperform native GST in stability and environmental adaptability. This approach provides a versatile platform for creating tunable and diverse protein assemblies with broad applications in antioxidant therapies and biomedical interventions.

Unraveling the Role of Polyoxometalates-Based Superchaotropes on the Photophysics of Organic Molecules and Modulation of Water Dynamics in a Hydrophilic Block Copolymer Solution

Polyoxometalates (POMs) are composed of nanometric metal-oxide anions and have rich solution chemistry. In this class, Keggin POMs have been identified as the most influential inorganic additives for aqueous nonionic soft matter systems. POMs being at the borderline of classical ions and charged colloids possess fascinating solution properties; the present work aims to delve deeper into the interactions between nanoions and nonionic soft matters from a spectroscopic point of view. Our studies reveal that although of the same structural makeup, silicotungstic acid hydrate (SiW) and phosphotungstic acid hydrate (PW) affect the photophysics of Coumarin-480 (C-480) in poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) ((PEO)76-(PPO)30-(PEO)76, F-68) copolymeric media in a dissimilar manner. From time-resolved studies, we find a preference for SiW toward the intramolecular charge transfer state of C-480, whereas PW favors the locally emissive state of the probe. Further, from rotational relaxation studies, it appears that SiW renders a rigid environment around the probe molecule, while PW relaxes the copolymeric environment. Finally, the dynamic quenching mechanism of the added nanoions was unraveled, which showed a straightforward Förster mechanism for SiW but a short-range interaction was operative for PW. From Fourier transform infrared and 1H NMR, it can be concluded that both the nanoions interacted with the PPO moiety of the copolymer; yet, their contrasting effect on the photophysics has been rationalized as a consequence of charge density on the ions.

Cobaltabis(dicarbollide) Interaction with DNA Resolved at the Atomic Scale

Boron neutron capture therapy represents a promising avenue for cancer treatment that requires nontoxic drugs with a high boron content efficiently distributed into cancerous cells. The metallacarborane o-cobaltabis(dicarbollide) ([COSAN]-) fulfills these requirements and constitutes an attractive candidate. Nevertheless, the interaction of this promising drug with nucleic acids, the assumed target of the biological damage, is poorly understood since contradictory results are reported in the literature. This work establishes the DNA/[COSAN]- interaction strength, mechanism, and time scale at the atomistic level by using a combination of microsecond-molecular dynamics and hybrid quantum mechanics/molecular mechanics simulations and by quantifying the absolute binding free energy. Results show that the DNA/[COSAN]- interaction is highly dependent on the ionic strength of the medium. A relatively weak DNA major groove binding (ΔGbind= -2.49 kcal/mol) driven mostly by dihydrogen B-H···H-N bonding is observed in the simulations only at a high NaCl concentration, whereas DNA intercalation mode is deemed highly unlikely.