Time Evolution of Ultrasmall Gold Nanoparticle-Protein Interactions

Thermodynamics and models for small nanoparticles upon protein adsorption

Proteins are some of the most important components in living organisms. When nanoparticles enter a living system, they swiftly interact with proteins to produce the so-called "protein corona", which depicts the adsorption of proteins on large nanoparticles (normally tens to hundreds of nanometers). However, the sizes of small nanoparticles (typically, fluorescent nanomaterials such as quantum dots, noble metal nanoclusters, carbon dots, etc.) are less than 10 nm, which are comparable or even much smaller than those of proteins. Can proteins also adsorb onto the surface of small nanoparticles to form a "protein corona"? In this perspective, the interactions between small nanoparticles with proteins are discussed in detail, including the main characterization methods and thermodynamic mechanisms. The interaction models are summarized. In particular, the concept of a "protein complex" is emphasized.

Diverse Role of Buffer Mediums and Protein Concentrations to Mediate the Multimodal Interaction of Phenylalanine-Functionalized Gold Nanoparticle and Lysozyme Protein at Same Nominal pH

Recently, buffer molecules have been known to affect intermolecular protein-protein interactions at physiological pH. However, the roles of buffer molecules and different monolayer protein concentrations remain elusive in controlling the interaction of gold nanoparticles (Au NPs) with protein molecules. Herein, for the first time taking phenylalanine functionalized gold nanoparticles (Au-Phe NPs) and lysozyme (Lyz) protein as model systems, we report that buffer molecules of different charges (at a particular pH) play diverse roles in protein-Au NPs interaction, particularly in protein induced Au NPs aggregation. Among different buffers, negatively charged buffer (citrate and phosphate) induces aggregation of both Au-Phe NPs and Lyz protein, whereas zwitterionic and positive buffer (HEPES, MOPS, and Tris) only cause the Au NPs aggregation. Taking the diverse role of buffer into account, we propose multimodal models for stability and protein induced aggregation mechanism of NPs at different monolayer (sub-, near-, and excess) concentrations of Lyz in different medium.

Realizing active targeting in cancer nanomedicine with ultrasmall nanoparticles

Ultrasmall nanoparticles (usNPs) have emerged as promising theranostic tools in cancer nanomedicine. With sizes comparable to globular proteins, usNPs exhibit unique physicochemical properties and physiological behavior distinct from larger particles, including lack of protein corona formation, efficient renal clearance, and reduced recognition and sequestration by the reticuloendothelial system. In cancer treatment, usNPs demonstrate favorable tumor penetration and intratumoral diffusion. Active targeting strategies, incorporating ligands for specific tumor receptor binding, serve to further enhance usNP tumor selectivity and therapeutic performance. Numerous preclinical studies have already demonstrated the potential of actively targeted usNPs, revealing increased tumor accumulation and retention compared to non-targeted counterparts. In this review, we explore actively targeted inorganic usNPs, highlighting their biological properties and behavior, along with applications in both preclinical and clinical settings.

Stealth and Biocompatible Gold Nanoparticles through Surface Coating with a Zwitterionic Derivative of Glutathione

Gold nanoparticles (AuNPs) hold promise in biomedicine, but challenges like aggregation, protein corona formation, and insufficient biocompatibility must be thoroughly addressed before advancing their clinical applications. Designing AuNPs with specific protein corona compositions is challenging, and strategies for corona elimination, such as coating with polyethylene glycol (PEG), have limitations. In this study, we introduce a commercially available zwitterionic derivative of glutathione, glutathione monoethyl ester (GSHzwt), for the surface coating of colloidal AuNPs. Particles coated with GSHzwt were investigated alongside four other AuNPs coated with various ligands, including citrate ions, tiopronin, glutathione, cysteine, and PEG. We then undertook a head-to-head comparison of these AuNPs to assess their behavior in biological fluid. GSHzwt-coated AuNPs exhibited exceptional resistance to aggregation and protein adsorption. The particles could also be readily functionalized with biotin and interact with streptavidin receptors in human plasma. Additionally, they exhibited significant blood compatibility and noncytotoxicity. In conclusion, GSHzwt provides a practical and easy method for the surface passivation of AuNPs, creating "stealth" particles for potential clinical applications.

Perspectives on Protein-Nanoparticle Interactions at the In Vivo Level

The distinct features of nanoparticles have provided a vast opportunity of developing new diagnosis and therapy strategies for miscellaneous diseases. Although a few nanomedicines are available in the market or in the translation stage, many important issues are still unsolved. When entering the body, nanomaterials will be quickly coated by proteins from their surroundings, forming a corona on their surface, the so-called protein corona. Studies have shown that the protein corona has many important biological implications, particularly at the in vivo level. For example, they can promote the immune system to rapidly clear these outer materials and prevent nanoparticles from playing their designed role in therapy. In this Perspective, the available techniques for characterizing protein-nanoparticle interactions are critically summarized. Effects of nanoparticle properties and environmental factors on protein corona formation, which can further regulate the in vivo fate of nanoparticles, are highlighted and discussed. Moreover, recent progress on the biomedical application of protein corona-engineered nanoparticles is introduced, and future directions for this important yet challenging research area are also briefly discussed.

Protein structure-function continuum model: Emerging nexuses between specificity, evolution, and structure

The rationale for replacing the old binary of structure-function with the trinity of structure, disorder, and function has gained considerable ground in recent years. A continuum model based on the expanded form of the existing paradigm can now subsume importance of both conformational flexibility and intrinsic disorder in protein function. The disorder is actually critical for understanding the protein-protein interactions in many regulatory processes, formation of membrane-less organelles, and our revised notions of specificity as amply illustrated by moonlighting proteins. While its importance in formation of amyloids and function of prions is often discussed, the roles of intrinsic disorder in infectious diseases and protein function under extreme conditions are also becoming clear. This review is an attempt to discuss how our current understanding of protein function, specificity, and evolution fit better with the continuum model. This integration of structure and disorder under a single model may bring greater clarity in our continuing quest for understanding proteins and molecular mechanisms of their functionality.