Surface modification of cowpea chlorotic mottle virus capsids via a copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction and their adhesion behavior with HeLa cells

Abstract

A copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction was exploited for the surface modification of cowpea chlorotic mottle virus (CCMV). The exposed carboxyl residues of the CCMV capsids were modified with an alkyne and then further modified with an azide, using a triazole connection in the presence of CuSO4, tris(2-carboxyethyl)phosphine hydrochloride (TCEP), and a bathocuproin disulfonic acid disodium salt (BCDS). Fluorogenic coumarin was successfully grafted onto the CCMV capsids and monitored by fast protein liquid chromatography (FPLC) and UV-irradiated SDS-PAGE. An oligo-ethylene glycol (OEG) short chain and an Arg-Gly-Asp (RGD) peptide were also connected to the CCMV capsids via the CuAAC reaction. Size-exclusion FPLC, transmission electron microscopy (TEM), and dynamic light scattering (DLS) analyses confirmed the modification and integrity of the viral capsids. Interestingly, OEG-CCMV displayed a unique phenomenon of connected bridges with the intact capsids crosslinked to each other. Coumarin-CCMV, OEG-CCMV, and RGD-CCMV were absorbed onto APTES slides for cell binding with HeLa cells. The opposite adhesion behavior of OEG-CCMV and RGD-CCMV indicated the inhibition effect of OEG and the promotion effect of RGD for cell attachment. This provides a generalized method for chemical modification of the surface of virus capsids with multivalent ligands, which demonstrates the potential applications in bioimaging, tissue engineering, and drug delivery.