Designed Rubredoxin miniature in a fully artificial electron chain triggered by visible light

Structural insights into temperature-dependent dynamics of METPsc1, a miniaturized electron-transfer protein

The design of protein-metal complexes is rapidly advancing, with applications spanning catalysis, sensing, and bioremediation. We report a comprehensive investigation of METPsc1, a Miniaturized Electron Transfer Protein, in complex with cadmium. This study elucidates the impact of metal coordination on protein folding and structural dynamics across temperatures from 100 K to 300 K. Our findings reveal that METPsc1, composed of two similar halves stabilized by intramolecular hydrogen bonds, exhibits a unique "clothespin-like" recoil mechanism. This allows it to adapt to metal ions of varying radii, mirroring the flexibility observed in natural rubredoxins. High-resolution crystallography and molecular dynamics simulations unveil concerted backbone motions and subtle temperature-dependent shifts in side-chain conformations, particularly for residues involved in crystal packing. Notably, CdS bond lengths increase with temperature, correlating with anisotropic motions of the sulfur atoms involved in second-shell hydrogen bonding. This suggests a dynamic role of protein matrix upon redox cycling. These insights into METPsc1 highlight its potential for catalysis and contribute to the designing of artificial metalloproteins with functional plasticity.

Turn-Adopting Peptidomimetic as a Formyl Peptide Receptor-1 Antagonist

The design, synthesis, and characterization of a new peptidomimetic acting as a formyl peptide receptor (FPR1) antagonist (N-19004) are herein reported. The molecule has been identified with docking studies of the highly potent FPR1 antagonist UPARANT on human receptor. N-19004 recapitulates all pharmacophoric groups necessary for recognition into a minimal structure, with a crucial role of the 2,6-diamino-thiophenyl scaffold mimicking the positions of Cα atoms of Arg residues in the turned Arg-Aib-Arg segment of UPARANT. N-19004 demonstrated to interfere with the biological properties of FPR1 both in vitro and in vivo. In a mouse model of choroidal neovascularization, N-19004 markedly reduced the size of laser-induced choroidal lesions, with reabsorption of the edema regions by a systemic administration route.

Catalytic Nanomaterials by Conjugation of an Artificial Heme-Peroxidase to Amyloid Fibrils

The self-assembly of proteins and peptides into fibrillar amyloid aggregates is a highly promising route to define the next generation of functional nanomaterials. Amyloid fibrils, traditionally associated with neurodegenerative diseases, offer exceptional conformational and chemical stability and mechanical properties, and resistance to degradation. Here, we report the development of catalytic amyloid nanomaterials through the conjugation of a miniaturized artificial peroxidase (FeMC6*a) to a self-assembling amyloidogenic peptide derived from human transthyretin, TTR(105-115), whose sequence is YTIAALLSPYS. Our synthetic approach relies on fast and selective click ligation upon proper modification of both the peptide and FeMC6*a, leading to TTRLys108@FeMC6*a. Mixing unmodified TTR(105-115) with TTRLys108@FeMC6*a allowed the generation of enzyme-loaded amyloid fibrils, namely, FeMC6*a@fibrils. Catalytic studies, performed in aqueous solution at nearly neutral pH, using ABTS as a model substrate and H2O2 as the oxidizing agent revealed that the enzyme retains its catalytic activity. Moreover, the activity was found to depend on the TTRLys108@FeMC6*a/unmodified TTR(105-115) peptide ratio. In particular, those with the 2:100 ratio showed the highest activity in terms of initial rates and substrate conversion among the screened nanoconjugates and compared to the freely diffusing enzyme. Finally, the newly developed nanomaterials were integrated into a flow system based on a polyvinylidene difluoride membrane filter. Within this flow-reactor, multiple reaction cycles were performed, showcasing the reusability and stability of the catalytic amyloids over extended periods, thus offering significantly improved characteristics compared to the isolated FeMC6*a in the application to a number of practical scenarios.

Application of artificial backbone connectivity in the development of metalloenzyme mimics

Metal-dependent enzymes are abundant and vital catalytic agents in nature. The functional versatility of metalloenzymes has made them common targets for improvement by protein engineering as well as mimicry by de novo designed sequences. In both strategies, the incorporation of non-canonical cofactors and/or non-canonical side chains has proved a useful tool. Less explored-but similarly powerful-is the utilization of non-canonical covalent modifications to the polypeptide backbone itself. Such efforts can entail either introduction of limited artificial monomers in natural chains to produce heterogeneous backbones or construction of completely abiotic oligomers that adopt defined folds. Herein, we review recent research applying artificial protein-like backbones in the construction of metalloenzyme mimics, highlighting progress as well as open questions in this emerging field.

Co(II) Substitution Enhances the Esterase Activity of a de Novo Designed Zn(II) Carbonic Anhydrase

Carbonic Anhydrases (CAs) have been a target for de novo protein designers due to the simplicity of the active site and rapid rate of the reaction. The first reported mimic contained a Zn(II) bound to three histidine imidazole nitrogens and an exogenous water molecule, hence closely mimicking the native enzymes' first coordination sphere. Co(II) has served as an alternative metal to interrogate CAs due to its d7 electronic configuration for more detailed solution characterization. We present here the Co(II) substituted [Co(II)(H2O/OH-)]N(TRIL2WL23H)3 n+ that behaves similarly to native Co(II) substituted human-CAs. Like the Zn(II) analogue, the cobalt-derivative at slightly basic pH is incapable of hydrolyzing p-nitrophenylacetate (pNPA); however, as the pH is increased a significant activity develops, which at pH values above 10 eventually yields a catalytic efficiency that exceeds that of the [Zn(II)(OH-)]N(TRIL2WL23H)3 + peptide complex. X-ray absorption analysis is consistent with an octahedral species at pH 7.5 that converts to a 5-coordinate species by pH 11. UV-vis spectroscopy can monitor this transition, giving a pKa for the conversion of 10.3. We assign this conversion to the formation of a 5-coordinate Co(II)(Nimid)3(OH)(H2O) species. The pH dependent kinetic analysis indicates the maximal rate (kcat), and thus the catalytic efficiency (kcat/Km), follow the same pH profile as the spectroscopic conversion to the pentacoordinate species. This correlation suggests that the chemically irreversible ester hydrolysis corresponds to the rate determining process.

MetalHawk: Enhanced Classification of Metal Coordination Geometries by Artificial Neural Networks

The chemical properties of metal complexes are strongly dependent on the number and geometrical arrangement of ligands coordinated to the metal center. Existing methods for determining either coordination number or geometry rely on a trade-off between accuracy and computational costs, which hinders their application to the study of large structure data sets. Here, we propose MetalHawk (https://github.com/vrettasm/MetalHawk), a machine learning-based approach to perform simultaneous classification of metal site coordination number and geometry through artificial neural networks (ANNs), which were trained using the Cambridge Structural Database (CSD) and Metal Protein Data Bank (MetalPDB). We demonstrate that the CSD-trained model can be used to classify sites belonging to the most common coordination numbers and geometry classes with balanced accuracy equal to 96.51% for CSD-deposited metal sites. The CSD-trained model was also found to be capable of classifying bioinorganic metal sites from the MetalPDB database, with balanced accuracy equal to 84.29% on the whole PDB data set and to 91.66% on manually reviewed sites in the PDB validation set. Moreover, we report evidence that the output vectors of the CSD-trained model can be considered as a proxy indicator of metal-site distortions, showing that these can be interpreted as a low-dimensional representation of subtle geometrical features present in metal site structures.

Dye Decolorization by a Miniaturized Peroxidase Fe-MimochromeVI*a

Oxidases and peroxidases have found application in the field of chlorine-free organic dye degradation in the paper, toothpaste, and detergent industries. Nevertheless, their widespread use is somehow hindered because of their cost, availability, and batch-to-batch reproducibility. Here, we report the catalytic proficiency of a miniaturized synthetic peroxidase, Fe-Mimochrome VI*a, in the decolorization of four organic dyes, as representatives of either the heterocyclic or triarylmethane class of dyes. Fe-Mimochrome VI*a performed over 130 turnovers in less than five minutes in an aqueous buffer at a neutral pH under mild conditions.