Inhibition of alpha-chymotrypsin by pristine single-wall carbon nanotubes: Clogging up the active site

The preferred spatial orientation of single-wall carbon nanotubes (SWCNTs) in their interaction with enzymes determines their behavior either as nano-supports or as inhibitors. alpha-chymotrypsin (alpha-CT) is considered a serine protease model for studying nanomaterial/proteases interactions. The interaction of alpha-CT with pristine single-wall carbon nanotubes is still unknown. Here alpha-CT/SWCNT hybrids are synthesized and characterized. Spectroscopic, microscopic and kinetic measurements, coupled to molecular dynamics simulations, provide a detailed description of the interaction between alpha-CT and SWCNTs. The SWCNT binding pocket was unambiguously identified. A perfect match is observed with the crevice structure of the alpha-CT substrate binding pocket. The activity of alpha-CT, upon SWCNT binding, is dramatically reduced, as expected by the interaction of the SWCNT in the active site of the protein. it-it stacking between aromatic residues and the conjugated surface of SWCNT governs alpha-CT/SWCNT interactions. An important role in the bonding appears also for purely hydrophobic residues and with residues able to establish surfactant-like interactions. The secondary structure of alpha-CT and the catalytic triad structure are not perturbed by the complex formation, on the contrary the volume of the substrate binding pocket is strongly reduced by SWCNT binding because SWCNT occupies the alpha-CT substrate binding site, clogging the active site. (C) 2020 Elsevier Inc. All rights reserved.