Surface PEGylation via native chemical ligation

Native chemical ligation (NCL) is an emerging chemoselective chemistry that forms an amide bond by trans-thioesterification followed by intramolecular nucleophilic rearrangement between thioester and cysteine. The reaction is simple, occurs in a mild aqueous solution, and gives near-quantitative yields of a desired product. Since the first report in 1994, most studies involving the use of NCL have focused on the total synthesis of proteins to address fundamental questions pertaining to many aspects of protein science, such as folding, mirror images, and site-specific labeling of proteins, but applications of the NCL reaction for other areas remain largely unexplored. Herein, we present a facile strategy for surface immobilization of poly(ethylene glycol) (PEG) utilizing the NCL reaction. Surface immobilization of PEG (i.e., PEGylation) plays a key role in preventing nonspecific protein adsorption on surfaces, which is crucial in a wide variety of medical devices. Using cysteine-PEG and thioester-containing phosphonic acid conjugates, we achieved efficient surface PEGylation on titanium surfaces. Ellipsometry, goniometry, and X-ray photoelectron spectroscopy (XPS) unambiguously confirmed the presence of PEGs, which provided nonfouling effects of surfaces. This study indicates that the NCL reaction will be a useful toolkit for surface bioconjugation and functionalization.