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Functional Immobilization of the Small GTPase Rab6A on DNA–Gold Nanoparticles by Using a Site‐Specifically Attached Poly(ethylene glycol) Linker and Thiol Place‐Exchange Reaction

Efficient strategies to achieve functional immobilization of biomacromolecules, such as proteins and DNA, on inorganic nanoparticles have been the subject of growing interest in recent years, since they form a basis for the rational design of functional nanomaterials. 2] These materials have a broad scope of application in bioanalytics and biomolecular electronics. However, the functional immobilization of proteins on nanoparticles is often difficult to achieve because the occurrence of multiple functional groups in proteins complicates the task of linking them to surfaces while keeping them fully functional. Commonly employed methods often take advantage of nonspecific absorption or covalent attachment. These strategies often lead to uncontrolled immobilization and random orientation of the proteins on the nanoparticle surface. One strategy to overcome the potential problems arising from these approaches is based on specific interactions between the protein and a functionalized nanoparticle surface. We report here on the controlled assembly of covalently linked protein–nanoparticle conjugates through an approach based on the highly specific modification of proteins with a functionalized poly(ethylene glycol) linker molecule by a native chemical ligation reaction (Scheme 1). Such PEGbased linkers are chemically inert and water soluble; this renders them highly attractive as solvent-exposed spacers that can easily react with nanoparticle surfaces through an appended thiol group. In this study, we investigated this strategy by using a small GTPase of the Rab family. Rab proteins are central regulators of vesicular transport and are involved in vesicular budding, targeting, and fusion. During their normal mode of action, these Rab proteins cycle between an active GTPand an inactive GDP-bound conformation; this imposes temporal and spatial regulation on membrane transport. Rab6 was originally identified as a key player of microtubule-dependent retrograde traffic, controlling vesicular trafficking from early endosomes to the trans-Golgi network, through the Golgi apparatus, and from the Golgi to the endoplasmatic reticulum,