In silico Validation of Pseudomonas aeruginosa Exotoxin A Domain I Interaction with the Novel Human scFv Antibody.

BACKGROUND: Pseudomonas (P.) aeruginosa is one of the leading causes of nosocomial infections. The pathogenicity of P. aeruginosa is related to its inherent antimicrobial resistance and the diverse virulence factors of this bacterium. Owing to the specific role of exotoxin A in P. aeruginosa pathogenesis, it is known as a promising therapeutic candidate to develop antibodies as an alternative to antibiotics. OBJECTIVE: The present study aimed to validate the interaction between a single-chain fragment variable (scFv) antibody identified from an scFv phage library against domain I exotoxin A by bioinformatic tools. METHODS: For this, several bioinformatics tools, including Ligplot, Swiss PDB viewer (SPDBV), PyMOL, I-TASSER, Gromacs, and ClusPro servers were used to evaluate the interaction of scFv antibody with P. aeruginosa exotoxin A. The I-TASSER server was utilized to predict the function and structure of proteins. The interaction of two proteins was analyzed using ClusPro tools. The best docking results were further analyzed with Ligplot, Swiss PDB viewer, and PyMOL. Consequently, molecular dynamics simulation was utilized to predict the stability of the secondary structure of the antibody and the binding energy of the scFv antibody to the domain I of exotoxin A. RESULTS: As a result, we demonstrated that data from computational biology could provide proteinprotein interaction information between scFv antibody/domain I exotoxin A and offers new insights into antibody development and therapeutic expansion. CONCLUSION: In summary, a recombinant human scFv capable of neutralizing P. aeruginosa exotoxin A is recommended as a promising treatment for infections caused by P. aeruginosa.

Isolation and characterizations of a novel recombinant scFv antibody against exotoxin A of Pseudomonas aeruginosa.

BACKGROUND: Pseudomonas aeruginosa is the leading cause of nosocomial infections, especially in people with a compromised immune system. Targeting virulence factors by neutralizing antibodies is a novel paradigm for the treatment of antibiotic-resistant pseudomonas infections. In this respect, exotoxin A is one of the most potent virulence factors in P. aeruginosa. The present study was carried out to identify a novel human scFv antibody against the P. aeruginosa exotoxin A domain I (ExoA-DI) from a human scFv phage library. METHODS: The recombinant ExoA-DI of P. aeruginosa was expressed in E. coli, purified by Ni-NTA column, and used for screening of human antibody phage library. A novel screening procedure was conducted to prevent the elimination of rare specific clones. The phage clone with high reactivity was evaluated by ELISA and western blot. RESULTS: Based on the results of polyclonal phage ELISA, the fifth round of biopanning leads to the isolation of several ExoA-DI reactive clones. One positive clone with high affinity was selected by monoclonal phage ELISA and used for antibody expression. The purified scFv showed high reactivity with the recombinant domain I and full-length native exotoxin A. CONCLUSIONS: The purified anti-exotoxin A scFv displayed high specificity against exotoxin A. The human scFv identified in this study could be the groundwork for developing a novel therapeutic agent to control P. aeruginosa infections.