title: Influence of the Surface Functional Group Density on the Carbon-Nanotube-Induced α-Chymotrypsin Structure and Activity Alterations.
abstract: Because of the special properties of carbon nanotubes (CNTs), their applications have been introduced to many fields. The biosafety of these emerging materials is of high concern concomitantly. Because CNTs may initially bind with proteins in biofluids before they exert biological effects, it is of great importance to understand how the target proteins interact with these exogenous nanomaterials. Here we investigated the interaction between α-chymotrypsin (α-ChT) and carboxylized multiwalled CNTs in a simulated biophysical environment utilizing the techniques of fluorescence, UV-vis, circular dichroism spectroscopy, ζ potential, atomic force microscopy, and bicinchoninic acid analysis. It was demonstrated that CNTs interacted with α-ChT through electrostatic forces, causing a decrement in the α-helix and an increment in the β-sheet content of the protein. The protein fluorescence was quenched in a static mode. The increase in the surface modification density of CNTs enhanced the protein absorption and decreased the enzymatic activity correspondingly. α-ChT activity inhibition induced by CNTs with low surface modification density exhibited noncompetitive characteristics; however, a competitive feature was observed when CNTs with high surface modification density interacted with the protein. An increase of the ionic strength in the reaction buffer may help to reduce the interaction between CNTs and α-ChT because the high ionic strength may favor the release of the protein from binding on a CNT surface modified with functional groups. Accordingly, the functionalization density on the CNT surface plays an important role in the regulation of their biological effects and is worthy of concern when new modified CNTs are developed.
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , Beijing 100085, P. R. China.
authors.forename: Xingchen
authors.initials: X
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , Beijing 100085, P. R. China.
authors.forename: Fang
authors.initials: F
authors.lastname: Hao
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , Beijing 100085, P. R. China.
authors.forename: Dawei
authors.initials: D
authors.lastname: Lu
authors.affiliation: Institute of Chemical Safety, Chinese Academy of Inspection and Quarantine , Beijing 100124, P. R. China.
authors.forename: Wei
authors.initials: W
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , Beijing 100085, P. R. China.
authors.forename: Qunfang
authors.initials: Q
authors.lastname: Zhou
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , Beijing 100085, P. R. China.
authors.forename: Guibin
authors.initials: G
authors.lastname: Jiang
mesh_terms: D055162:Biocatalysis; D002918:Chymotrypsin / Q000737:chemistry / Q000378:metabolism*; D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D018625:Microscopy, Atomic Force; D037742:Nanotubes, Carbon / Q000737:chemistry*; D009994:Osmolar Concentration; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D037742:Nanotubes, Carbon; D002918:Chymotrypsin; C117608:alpha-chymotrypsin
keywords: carbon nanotubes; enzymatic activity; functionalization density; protein structure; α-chymotrypsin