Solvent assistance in regiospecific disulfide formation in dimethylsulfoxide

Improved Expression of a Thermostable GH18 Bacterial Chitinase in Two Different Escherichia coli Strains and Its Potential Use in Plant Protection and Biocontrol of Phytopathogenic Fungi

Chitinases are enzymes that can break down chitin, a major component of the exoskeleton of insects and fungi. This feature makes them potential biopesticides in agriculture since they are considered a safe and environmentally friendly alternative to synthetic pesticides. In this work, we performed a comparative study between two different bacterial expression strains to produce a recombinant chitinase with improved stability. Escherichia coli strains Origami B and BL21 (DE3) were selected for their distinct cytosolic environment to express BhChitA chitinase of Bacillus halodurans C-125 and to investigate the role of disulfide bond formation and proper folding on its stability and activity. Expression of the recombinant BhChitA in bacterial strain containing oxidative cytosol (Origami B) improved its activity and stability. Although both expression systems have comparable biochemical properties (temperature range 20-80 °C and pH spectrum 3-10), BhChitA expressed in Origami strain seems more stable than expressed in BL21. Furthermore, the optimal expression conditions of the recombinant BhChitA has been carried out at 30 °C during 6 h for the Origami strain, against 20 °C during 2 h for BL21. On the other hand, no significant differences were detected between the two enzymes when the effect of metal ions was tested. These findings correlate with the analysis of the overall structure of BhChitA. The model structure permitted to localize disulfide bond, which form a stable connection between the substrate-binding residues and the hydrophobic core. This link is required for efficient binding of the chitin insertion domain to the substrate. BhChitA exhibited in vitro antifungal effect against phytopathogenic fungi and suppressed necrosis of Botrytis cinerea on detached tomato leaves. In vitro assays showed the influence of BhChitA on growth suppression of Botrytis cinerea (53%) Aspergillus niger (65%), Fusarium graminearum (25%), and Fusarium oxysporum (34%). Our results highlight the importance of the bacterial expression system with oxidative cytosol in producing promising biopesticides that can be applied for post-harvest processing and crop protection.

Lung Surfactant Protein B Peptide Mimics Interact with the Human ACE2 Receptor

Lung surfactant is a complex mixture of phospholipids and surfactant proteins that is produced in alveolar type 2 cells. It prevents lung collapse by reducing surface tension and is involved in innate immunity. Exogenous animal-derived and, more recently, synthetic lung surfactant has shown clinical efficacy in surfactant-deficient premature infants and in critically ill patients with acute respiratory distress syndrome (ARDS), such as those with severe COVID-19 disease. COVID-19 pneumonia is initiated by the binding of the viral receptor-binding domain (RBD) of SARS-CoV-2 to the cellular receptor angiotensin-converting enzyme 2 (ACE2). Inflammation and tissue damage then lead to loss and dysfunction of surface activity that can be relieved by treatment with an exogenous lung surfactant. Surfactant protein B (SP-B) is pivotal for surfactant activity and has anti-inflammatory effects. Here, we study the binding of two synthetic SP-B peptide mimics, Super Mini-B (SMB) and B-YL, to a recombinant human ACE2 receptor protein construct using molecular docking and surface plasmon resonance (SPR) to evaluate their potential as antiviral drugs. The SPR measurements confirmed that both the SMB and B-YL peptides bind to the rhACE2 receptor with affinities like that of the viral RBD-ACE2 complex. These findings suggest that synthetic lung surfactant peptide mimics can act as competitive inhibitors of the binding of viral RBD to the ACE2 receptor.

Two-Helix Supramolecular Proteomimetic Binders Assembled via PNA-Assisted Disulfide Crosslinking

Peptidic motifs folded in a defined conformation are able to inhibit protein-protein interactions (PPIs) covering large interfaces and as such they are biomedical molecules of interest. Mimicry of such natural structures with synthetically tractable constructs often requires complex scaffolding and extensive optimization to preserve the fidelity of binding to the target. Here, we present a novel proteomimetic strategy based on a 2-helix binding motif that is brought together by hybridization of peptide nucleic acids (PNA) and stabilized by a rationally positioned intermolecular disulfide crosslink. Using a solid phase synthesis approach (SPPS), the building blocks are easily accessible and such supramolecular peptide-PNA helical hybrids could be further coiled using precise templated chemistry. The elaboration of the structural design afforded high affinity SARS CoV-2 RBD (receptor binding domain) binders without interference with the underlying peptide sequence, creating a basis for a new architecture of supramolecular proteomimetics.

Emulation of the structure of the Saposin protein fold by a lung surfactant peptide construct of surfactant Protein B

The three-dimensional structure of the synthetic lung Surfactant Protein B Peptide Super Mini-B was determined using an integrative experimental approach, including mass spectrometry and isotope enhanced Fourier-transform infrared (FTIR) spectroscopy. Mass spectral analysis of the peptide, oxidized by solvent assisted region-specific disulfide formation, confirmed that the correct folding and disulfide pairing could be facilitated using two different oxidative structure-promoting solvent systems. Residue specific analysis by isotope enhanced FTIR indicated that the N-terminal and C-terminal domains have well defined α-helical amino acid sequences. Using these experimentally derived measures of distance constraints and disulfide connectivity, the ensemble was further refined with molecular dynamics to provide a medium resolution, residue-specific structure for the peptide construct in a simulated synthetic lung surfactant lipid multilayer environment. The disulfide connectivity combined with the α-helical elements stabilize the peptide conformationally to form a helical hairpin structure that resembles critical elements of the Saposin protein fold of the predicted full-length Surfactant Protein B structure.

Chemical methods for producing disulfide bonds in peptides and proteins to study folding regulation

Disulfide bonds play a critical role in the folding of secretory and membrane proteins. Oxidative folding reactions of disulfide bond-containing proteins typically require several hours or days, and numerous misbridged disulfide isomers are often observed as intermediates. The rate-determining step in refolding is thought to be the disulfide-exchange reaction from nonnative to native disulfide bonds in folding intermediates, which often precipitate during the refolding process because of their hydrophobic properties. To overcome this, chemical additives or a disulfide catalyst, protein disulfide isomerase (PDI), are generally used in refolding experiments to regulate disulfide-coupled peptide and protein folding. This unit describes such methods in the context of the thermodynamic and kinetic control of peptide and protein folding, including (1) regulation of disulfide-coupled peptides and protein folding assisted by chemical additives, (2) reductive unfolding of disulfide-containing peptides and proteins, and (3) regulation of disulfide-coupled peptide and protein folding using PDI.

Folding of peptides and proteins: role of disulfide bonds, recent developments

Disulfide-containing proteins are ideal models for studies of protein folding as the folding intermediates can be observed, trapped, and separated by HPLC during the folding reaction. However, regulating or analyzing the structures of folding intermediates of peptides and proteins continues to be a difficult problem. Recently, the development of several techniques in peptide chemistry and biotechnology has resulted in the availability of some powerful tools for studying protein folding in the context of the structural analysis of native, mutant proteins, and folding intermediates. In this review, recent developments in the field of disulfide-coupled peptide and protein folding are discussed, from the viewpoint of chemical and biotechnological methods, such as analytical methods for the detection of disulfide pairings, chemical methods for disulfide bond formation between the defined Cys residues, and applications of diselenide bonds for the regulation of disulfide-coupled peptide and protein folding.

A chemical method for investigating disulfide-coupled peptide and protein folding

Investigations of protein folding have largely involved studies using disulfide-containing proteins, as disulfide-coupled folding of proteins permits the folding intermediates to be trapped and their conformations determined. Over the last decade, a combination of new biotechnical and chemical methodology has resulted in a remarkable acceleration in our understanding of the mechanism of disulfide-coupled protein folding. In particular, expressed protein ligation, a combination of native chemical ligation and an intein-based approach, permits specifically labeled proteins to be easily produced for studies of protein folding using biophysical methods, such as NMR spectroscopy and X-ray crystallography. A method for regio-selective formation of disulfide bonds using chemical procedures has also been established. This strategy is particularly relevant for the study of disulfide-coupled protein folding, and provides us not only with the native conformation, but also the kinetically trapped topological isomer with native disulfide bonds. Here we review recent developments and applications of biotechnical and chemical methods to investigations of disulfide-coupled peptide and protein folding. Chemical additives designed to accelerate correct protein folding and to avoid non-specific aggregation are also discussed.