Carbon Nanotube Wins the Competitive Binding over Proline-Rich Motif Ligand on SH3 Domain

The binding competition between a proline-rich motif (PRM) ligand and a hydrophobic nanoparticle, the single-wall carbon nanotube (SWCNT), at the binding pocket of SH3 domain, has been investigated by molecular dynamics simulations. It is found that the SWCNT has a very high probability of occupying the binding pocket of the SH3 domain, which prevents the PRM ligand from binding to the pocket. The binding free energy landscapes show that the SWCNT has similar to 0.6 kcal/mol stronger binding affinity than the ligand in the three-way binding competition (SWCNT + ligand + protein). The potent binding affinity between the SWCNT and the SH3 domain is shown to be mainly from the pi-pi stacking interactions between the CNT and aromatic residues in the binding pocket. Our findings show that the existence of hydrophobic particles can greatly reduce the possibility of the regular binding of the ligand with the target protein, suggesting potential toxicity to proteins by hydrophobic nanoscale particles.