Are Pro8/Pro18 really critical for functional dynamic behavior of human endostatin N-terminal peptide? A comparative molecular dynamics study

Endostatin which is derived from the non-collagenous domain 1 of collagen XVIII and is a recently identified broad spectrum anti-angiogenesis agent, inhibits 65 different tumor types. The N-terminal fragment of endostatin protein (ES) has the same antitumor, antimigration and antipermeability effects as the entire protein. In the current study, we modeled two mutant variants of ES with two mutation sites (M1-ES (Pro(8)-> Ala) and M2-ES (Pro(18)-> Ala)) and tried to understand proline's effect on the peptide structure/stability by introducing P(8)A/ P(18)A mutations, and then in order to gain functional insight into mutation caused by amino acid substitution to the peptide structure/function, these effects were predicted using computational tools. From the RMSD analyses, it can be concluded that dynamic behavior of wild-type and mutant structures was not significantly different from each other and all systems reached equilibrium. The RMSF analysis also revealed that the M2-ES has smaller overall flexibility than the WT-ES and M1-ES structures. The radius of gyration analysis then confirmed the structure of M2-ES compared to wild-type and M1 variant becomes more compact during simulation of our systems. Finally, molecular dynamics simulation analysis shows that replacement of Pro residue with Ala is able to induce a distinct beta-sheet in both mutant structures. Indeed, the docking analysis shows the WT-ES and M2-ES bind to the same region of alpha(v)beta(3) integrin, suggesting similar interaction pattern with a relatively equal binding energy into this receptor. Our results speculated that the P(8)A/ P(18)A replacements confer no improvement (or no tangible weakness) in the peptide biological activity although is able to change structural conformation of N-terminal fragment of human endostatin protein.