Improving the antimicrobial activity of RP9 peptide through theoretical and experimental investigation.

Future threats to humanity may stem from the rise of antimicrobial resistance, which has compromised the effectiveness of existing antibiotics. Antimicrobial peptides possess the ability to directly eliminate pathogens and cancer cells, generally without the development of resistance. Among these peptides is RP9 (RGSALTHLP), derived from the white blood cells of crocodiles. In this research, three mutations were initially designed: LR-mut (RGSALTHLR), KR-mut (RGSAKTHLR), and WP-mut (RGSAWTHLP). The physicochemical characteristics of these peptides were assessed, revealing that KR-mut exhibited the most favorable biophysical properties. Subsequently, twenty molecular dynamics simulations were conducted for all peptides in pure water and at four different octanol concentrations (30 %, 50 %, 70 %, and 100 %) to evaluate their biophysical attributes. The findings from the 4000 ns molecular dynamics simulations revealed that the KR-mut exhibited reduced values of RMSD, the radius of gyration, solvent accessible surface area, and RMSF, while simultaneously showing an increased number of hydrogen bonds and interactions with water molecules. This peptide also showed the lowest free energy of solvation and the highest solubility across various octanol concentrations compared to the other peptides. The results obtained from the biophysical assessments and molecular dynamics simulations were consistent, resulting in the conclusion that KR-mut is expected to exhibit superior antibacterial activity compared to both the other mutated peptides and the wild type peptides. These theoretical findings were validated through experimental minimum inhibitory concentration (MIC) tests on gram-negative