High-Fidelity Protein Targeting into Membrane Lipid Microdomains in Living Cells

Proximity Enzymatic Glyco-Remodeling Enables Direct and Highly Efficient Lipid Raft Imaging on Live Cells

Lipid rafts, highly ordered cell membrane domains mainly composed of cholesterol, sphingolipids, and protein receptors, serve as important functional platforms for regulation of lipid/protein interactions. The major predicament in lipid raft study is the lack of direct and robust visualization tools for in situ tracking raft components. To solve this issue, we herein report a proximity enzymatic glyco-remodeling strategy for direct and highly efficient lipid raft labeling and imaging on live cells. Through cofunctionalization of raft-specific recognition motif and glycan-remodeling enzyme on gold nanoparticles, the fabricated nanoprobe can be specifically guided to the raft domains to perform catalytic remodeling on neighboring glycans. Taking advantage of the abundant glycoconjugates enriched in lipid rafts, this elaborate design achieves the translation of one raft-recognition event to multiple raft-confined labeling operations, thus, significantly increasing the labeling efficiency and imaging sensitivity. The direct covalent labeling also enables in situ and long-term tracking of raft components in live cells. The method possesses broad applicability and potential expansibility, thus, will greatly facilitate the investigations on the complex composition, organization, and dynamics of lipid rafts.

Self-assembly of robust gold nanoparticle monolayer architectures for quantitative protein interaction analysis by LSPR spectroscopy

Localized surface plasmon resonance (LSPR) detection offers highly sensitive label-free detection of biomolecular interactions. Simple and robust surface architectures compatible with real-time detection in a flow-through system are required for broad application in quantitative interaction analysis. Here, we established self-assembly of a functionalized gold nanoparticle (AuNP) monolayer on a glass substrate for stable, yet reversible immobilization of Histidine-tagged proteins. To this end, one-step coating of glass substrates with poly-L-lysine graft poly(ethylene glycol) functionalized with ortho-pyridyl disulfide (PLL-PEG-OPSS) was employed as a reactive, yet biocompatible monolayer to self-assemble AuNP into a LSPR active monolayer. Site-specific, reversible immobilization of His-tagged proteins was accomplished by coating the AuNP monolayer with tris-nitrilotriacetic acid (trisNTA) PEG disulfide. LSPR spectroscopy detection of protein binding on these biocompatible functionalized AuNP monolayers confirms high stability under various harsh analytical conditions. These features were successfully employed to demonstrate unbiased kinetic analysis of cytokine-receptor interactions.