Computer simulations were performed to study the antimicrobial peptide microcin J25 (MJ25), a 21-mer peptide with an unusual lasso structure and high activity against Gram-negative bacteria. MJ25 has intracellular targets. The initial step of MJ25 acquisition in bacterial cells is binding to the outer-membrane receptor FhuA. Molecular dynamics simulations were implemented to study the binding mechanism of MJ25 to FhuA and to search for important binding residues. The absolute binding free energy calculated from combined free energy perturbation and thermodynamic integration methods agrees well with experimental data. In addition, computational mutation analysis revealed that His5 is the key residue responsible for MJ25 and FhuA association. We found that the number of hydrogen bonds is essential for binding of MJ25 to FhuA. This atomistic, quantitative insight sheds light on the mechanism of action of MJ25 and may pave a path for designing active MJ25 analogues.
Bibliographical noteFunding Information:
This work was supported by the National Institutes of Health (Grant GM111358) and the National Science Foundation (Grant CBET-1412283). We acknowledge computational support from the Minnesota Supercomputing Institute (MSI) and the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by the National Science Foundation (Grant ACI-10535753). Support from the University of Minnesota Digital Technology Center and the University of Minnesota Institute for Engineering in Medicine is also acknowledged.