L-RAR systems. The binding modes of the tripeptide RAR in all systems were observed and compared to investigate the changes due to the mutated residues. More number of hydrogen bonds was observed between the protein and bound substrate compared to the L-LTA4 systems because of the high number of polar hydrogen in the peptide substrate. In the WT system, strong molecular interactions were observed through the hydrogen bonds and p-cation interactions formed between protein and substrate ( Figure 8A ). The C-terminal carboxylate which is equivalent to the carboxylate of LTA4 has formed strong hydrogen bond interactions with both positively charged residues R563 and K565, the carboxylate recognition sites. These interactions mainly hold the RAR at the active site and improve its binding strength. As reported, the N-terminal amino group interacted with the E271 which is the N-terminal recognition site for the peptide substrates.