Design of High-Affinity Metal-Controlled Protein Dimers

Metals at the Helm: Revolutionizing Protein Assembly and Applications

Protein assembly is an essential process in biological systems, where proteins self-assemble into complex structures with diverse functions. Inspired by the exquisite control over protein assembly in nature, scientists have been exploring ways to design and assemble protein structures with precise control over their topologies and functions. One promising approach for achieving this goal is through metal coordination, which utilizes metal-binding motifs to mediate protein-protein interactions and assemble protein complexes with controlled stoichiometry and geometry. Metal coordination provides a modular and tunable approach for protein assembly and de novo structure design, where the metal ion acts as a molecular glue that holds the protein subunits together in a specific orientation. Metal-coordinated protein assemblies have shown great potential for developing functional metalloproteinase, novel biomaterials and integrated drug delivery systems. In this review, an overview of the recent advances in protein assemblies benefited from metal coordination is provided, focusing on various protein arrangements in different dimensions including protein oligomers, protein nanocage and higher-order protein architectures. Moreover, the key metal-binding motifs and strategies used to assemble protein structures with precise control over their properties are highlighted. The potential applications of metal-mediated protein assemblies in biotechnology and biomedicine are also discussed.

Biofabrication of functional protein nanoparticles through simple His-tag engineering

We have developed a simple, robust, and fully transversal approach for the a-la-carte fabrication of functional multimeric nanoparticles with potential biomedical applications, validated here by a set of diverse and unrelated polypeptides. The proposed concept is based on the controlled coordination between Zn2+ ions and His residues in His-tagged proteins. This approach results in a spontaneous and reproducible protein assembly as nanoscale oligomers that keep the original functionalities of the protein building blocks. The assembly of these materials is not linked to particular polypeptide features, and it is based on an environmentally friendly and sustainable approach. The resulting nanoparticles, with dimensions ranging between 10 and 15 nm, are regular in size, are architecturally stable, are fully functional, and serve as intermediates in a more complex assembly process, resulting in the formation of microscale protein materials. Since most of the recombinant proteins produced by biochemical and biotechnological industries and intended for biomedical research are His-tagged, the green biofabrication procedure proposed here can be straightforwardly applied to a huge spectrum of protein species for their conversion into their respective nanostructured formats.

Insights on the emerging biotechnology of histidine-rich peptides

In the late 70's, the discovery of the restriction enzymes made possible the biological production of functional proteins by recombinant DNA technologies, a fact that largely empowered both biotechnological and pharmaceutical industries. Short peptides or small protein domains, with specific molecular affinities, were developed as purification tags in downstream processes to separate the target protein from the culture media or cell debris, upon breaking the producing cells. Among these tags, and by exploiting the interactivity of the imidazole ring of histidine residues, the hexahistidine peptide (H6) became a gold standard. Although initially used almost exclusively in protein production, H6 and related His-rich peptides are progressively proving a broad applicability in novel utilities including enzymatic processes, advanced drug delivery systems and diagnosis, through a so far unsuspected adaptation of their binding capabilities. In this context, the coordination of histidine residues and metals confers intriguing functionalities to His-rich sequences useable in the forward-thinking design of protein-based nano- and micro-materials and devices, through strategies that are comprehensively presented here.

Developing Protein-Antitumoral Drug Nanoconjugates as Bifunctional Antimicrobial Agents

A novel concept about bifunctional antimicrobial drugs, based on self-assembling protein nanoparticles, has been evaluated here over two biofilm-forming pathogens, namely Pseudomonas aeruginosa and Staphylococcus aureus. Two structurally different antimicrobial peptides (GWH1 and PaDBS1R1) were engineered to form regular nanoparticles of around 35 nm, to which the small molecular weight drug Floxuridine was covalently conjugated. Both the assembled peptides and the chemical, a conventional cytotoxic drug used in oncotherapy, showed potent antimicrobial activities that were enhanced by the combination of both molecules in single pharmacological entities. Therefore, the resulting prototypes show promises as innovative nanomedicines, being potential alternatives to conventional antibiotics. The biological performance and easy fabrication of these materials fully support the design of protein-based hybrid constructs for combined molecular therapies, expected to have broad applicability beyond antimicrobial medicines. In addition, the approach taken here validates the functional exploration and repurposing of antitumoral drugs, which at low concentrations perform well as unexpected biofilm-inhibiting agents.

Divalent Cations: A Molecular Glue for Protein Materials

Among inorganic materials, divalent cations modulate thousands of physiological processes that support life. Their roles in protein assembly and aggregation are less known, although they are progressively being brought to light. We review the structural roles of divalent cations here, as well as the novel protein materials that are under development, in which they are used as glue-like agents. More specifically, we discuss how mechanically stable nanoparticles, fibers, matrices, and hydrogels are generated through their coordination with histidine-rich proteins. We also describe how the rational use of divalent cations combined with simple protein engineering offers unexpected and very simple biochemical approaches to biomaterial design that might address unmet clinical needs in precision medicine.