Extended ɛ34 Phage TSP Renatures After Urea-acid Unfolding

In antimicrobial-peptide/protein engineering, understanding the peptide/protein’s adaptability to harsh environmental conditions such as urea, proteases, fluctuating temperatures, high salts provide enormous insight into the pharmacokinetics and pharmacodynamics of the engineered peptide/protein and its ability to survive the harsh internal environment of the human body such as the gut or the harsh external environment to which they are applied. A previous work in our laboratory demonstrated that our cloned Eɛ34 TSP showed potent antimicrobial activity against Salmonella newington, and more so, could prevent biofilm formation on decellularized tissue. In this work, the effects of urea-acid on the Eɛ34 stability is studied, and the results demonstrates that at lower pHs of 3 and 4 with urea the protein was denatured into monomeric species. However, the protein withstood urea denaturation above pH of 5 and thus remained as trimeric protein. The mechanism of denaturation of Eɛ34 TSP seems to show that urea denatures proteins by depleting hydrophobic core of the protein by directly binding to the amide units via hydrogen bonds. The results of our in-silico investigation determined that urea binds with Eɛ34 TSP with relative free energies range of -3.4 to -2.9 kcal/mol at the putative globular head binding domain of the protein. The urea molecules interacts with with the protein’s predicted hydrophobic core, thus, disrupting and exposing the shielded hydrophobic moieties of Eɛ34 TSP to the solvent. We further showed that after the unfolding of Eɛ34 TSP via urea-acid, renaturation of the protein to its native conformation was possible within few hours. This unique characteristic of refolding of Eɛ34 TSP which is similar to that of the P22 phage tailspike protein is of special interest to protein scientists and can also be exploited in antimicrobial-protein engineering.

Ɛ34 Phage Tailspike Protein is Resistant to Trypsin and Inhibits and Salmonella Biofilm Formation

Salmonella can cause acute and chronic infections in humans. Salmonella species are known to cause food poisoning and other diseases in developing countries. Their role in the pathogenesis of these diseases has received increased international attention. Despite numerous advances in sanitation, they still can infect humans and cause outbreaks in developed countries. For example, Salmonella causes about 1.2 million illnesses in the US each year with over 450 deaths. Additionally, Salmonella outbreaks cause significant losses to chicken producers globally. The Salmonella species is also prone to acquiring resistance to various classes of antibiotics. Hence, the need for a paradigm shift from antibiotics to bacteriophages to manage, control and treat bacterial infections. The ɛ34 phage belongs to Podoviruses and categorized into the P22-like phages. The P22-like phages include ɛ34, ES18, P22, ST104, and ST64T. In this work, we investigated the antibacterial property of ɛ34 phage tailspike protein against Salmonella newington (S. newington). We demonstrate here that, the phage’s tailspike protein enzymatic property as a LPS hydrolase synergizes with Vero Cell culture supernatant in killing S. newington. Using decellularized cartilage scaffold as an ex vivo tissue model, the ɛ34 TSP protected the scaffold from S. newington biofilm formation. Computational analysis of the ɛ34 TSP interaction with membrane proteins of S. newington demonstrated a higher probability (0.7318) of binding to ompA of S. newington, and when docked to ompA extracellular component, it produced a high free energy of -11.3kcal/mol. We also demonstrate the resistance/sensitivity of the tailspike to the digestive enzyme trypsin. The data obtained in this work indicates that the trypsin resistant tailspike protein of Ɛ34 phage can be formulated as a novel antibacterial agent against S. newington.

The Ɛ34 Phage Tailspike Protein: An in vitro characterization, Structure Prediction, Potential Interaction with S. newington LPS and Cytotoxicity Assessment to Animal Cell Line.

The E34 phage is a member of the podoviridae family of phages, (short non-contractile tailed bacteriophages) that uses Salmonella newington as its host. This phage initiates the infection of its host via a specific interaction between its tailspike protein (TSP) and the lipopolysaccharides (LPS) of the bacterial. The E34 TSP is structurally similar and functionally equivalent to the P22 phage whose TSP has been well characterized and electron micrographs of both phages appear indistinguishable. The crystal structure of P22 phage TSP in complex with the O-antigen of S. typhimurium has been determined; and the active site of the TSP demonstrated to be the residues Asp392, Asp395 and Glu359 of the receptor binding domain. In another phage called E15, a phylogenetic relative of E34 phage, a short polysaccharide consisting of alpha-Gal-Man-Rha repeating units is responsible for the interaction between the E15 phage and Salmonella anatum LPS leading to the adsorption of the phage to the bacteria. Studies on E34 phage shows that it interacts with Salmonella newington O antigen polysaccharide component of the LPS, this polysaccharide consists of mannosyl-rhamnosyl-galactose repeating units joined together by beta-galactosyl linkages. However, no data exist regarding the specific residues of E34 TSP that are responsible for LPS binding and hydrolysis. In this study, the tailspike gene was cloned onto vector pET30a-LIC and expressed as a fusion protein termed the extended E34 TSP (EE34 TSP). We characterized the protein based on resistance to heat, SDS, and proteases; showing that the protein is heat resistant, shows aberrant electrophoretic mobility in the presence of SDS gradient, and actively binds to P22 phage heads to form hybrid phages that cannot infect P22 host. We also demonstrate via in silico study that the E34 TSP binds to and hydrolyses the O-antigen of its host via the ALA250, SER279 and ASP280 residues. Finally, testing E34 phage ability to protect Vero cells from Salmonella infection shows highly encouraging results, implying that E34 phage can be used in therapeutic or preventive medicine.

Perturbation of ACE2 structural ensembles by SARS-CoV-2 spike protein binding

The human ACE2 enzyme serves as a critical first recognition point of coronaviruses, including SARS-CoV-2. In particular, the extracellular domain of ACE2 interacts directly with the S1 tailspike protein of the SARS-CoV-2 virion through a broad protein-protein interface. Although this interaction has been characterized by X-ray crystallography and Cryo-EM, these structures do not reveal significant differences in ACE2 structure upon S1 protein binding. In this work, using several all-atom molecular dynamics simulations, we show persistent differences in ACE2 structure upon binding. These differences are determined with the Linear Discriminant Analysis (LDA) machine learning method and validated using independent training and testing datasets, including long trajectories generated by D. E. Shaw Research on the Anton 2 supercomputer. In addition, long trajectories for 78 potent ACE2-binding compounds, also generated by D. E. Shaw Research, were projected onto the LDA classification vector in order to determine whether the ligand-bound ACE2 structures were compatible with S1 protein binding. This allows us to predict which compounds are “apo-like” vs “complex-like”, as well as to pinpoint long-range ligand-induced allosteric changes of ACE2 structure.

Increasing the Affinity of an O-Antigen Polysaccharide Binding Site in Shigella Flexneri Bacteriophage Sf6 Tailspike Protein

We analysed the tailspike from bacteriophage Sf6 in complex with the O-polysaccharide of the pathogen Shigella flexneri. The conformational space populated by the polyrhamnose backbone of the S. flexneri O-polysaccharide as studied by an octasaccharide in complex with Sf6TSP could be well described with 2D 1H,1H-trNOESY NMR, utilizing a combination of methine-methine and methine-methyl correlations. The results are in good agreement with the conformations obtained from molecular dynamics (MD) simulations. To examine the impact of amino acid exchanges in the glycan binding site of Sf6TSP, MD simulations were used to predict increased O-polysaccharide binding affinities. We used surface plasmon resonance on S. flexneri O-polysaccharide surfaces to measure affinity increases in the obtained mutants. <br>

Increasing the Affinity of an O-Antigen Polysaccharide Binding Site in Shigella Flexneri Bacteriophage Sf6 Tailspike Protein

We analysed the tailspike from bacteriophage Sf6 in complex with the O-polysaccharide of the pathogen Shigella flexneri. The conformational space populated by the polyrhamnose backbone of the S. flexneri O-polysaccharide as studied by an octasaccharide in complex with Sf6TSP could be well described with 2D 1H,1H-trNOESY NMR, utilizing a combination of methine-methine and methine-methyl correlations. The results are in good agreement with the conformations obtained from molecular dynamics (MD) simulations. To examine the impact of amino acid exchanges in the glycan binding site of Sf6TSP, MD simulations were used to predict increased O-polysaccharide binding affinities. We used surface plasmon resonance on S. flexneri O-polysaccharide surfaces to measure affinity increases in the obtained mutants. <br>

Bacteriophage Sf6 Tailspike Protein for Detection of Shigella flexneri Pathogens

Bacteriophage research is gaining more importance due to increasing antibiotic resistance. However, for treatment with bacteriophages, diagnostics have to be improved. Bacteriophages carry adhesion proteins, which bind to the bacterial cell surface, for example tailspike proteins (TSP) for specific recognition of bacterial O-antigen polysaccharide. TSP are highly stable proteins and thus might be suitable components for the integration into diagnostic tools. We used the TSP of bacteriophage Sf6 to establish two applications for detecting Shigella flexneri (S. flexneri), a highly contagious pathogen causing dysentery. We found that Sf6TSP not only bound O-antigen of S. flexneri serotype Y, but also the glucosylated O-antigen of serotype 2a. Moreover, mass spectrometry glycan analyses showed that Sf6TSP tolerated various O-acetyl modifications on these O-antigens. We established a microtiter plate-based ELISA like tailspike adsorption assay (ELITA) using a Strep-tag®II modified Sf6TSP. As sensitive screening alternative we produced a fluorescently labeled Sf6TSP via coupling to an environment sensitive dye. Binding of this probe to the S. flexneri O-antigen Y elicited a fluorescence intensity increase of 80% with an emission maximum in the visible light range. The Sf6TSP probes thus offer a promising route to a highly specific and sensitive bacteriophage TSP-based Shigella detection system.