(349d) "Award Submission" Nanoscale Patterning of Membrane-Bound Proteins Formed Through Curvature-Induced Partitioning of Phase-Specific Receptor Lipids

Lipid mixtures self-assemble to form planar bilayers containing coexisting lipid phases in many compositional regimes. Coexisting lipid phases each have distinct compositions that can selectively partition optically active dyes, ligands, and membrane proteins. Therefore, precise arrangements of these phases in continuous lipid bilayers could be used to create displays of proteins, DNA strands, optically, chemically, or electrically active molecules, or nanoparticles.   Curvature-based sorting of functionalized lipids that comprise or partition into specific lipid phases could serve as a way of templating active molecules. A variety of methods have been developed to attach functional molecules to lipid headgroups.  These include covalent bonding and linkers such as single-stranded DNA, biotin, and glycan-phosphatidyl inositol.  Lipid headgroups can also be functionalized with a metal chelate group such as iminodiacetic acid (IDA) and nitrilotriacetic acid (NTA).  These chelate groups coordinate to divalent transition-metal ions such as Cu²⁺, Ni²⁺, and Zn²⁺ and sequester proteins rich with histidine moieties. This work describes a technique for forming high-density arrays and patterns of membrane-bound proteins through binding to a curvature-organized compositional pattern of metal-chelating lipids (Cu²⁺-DOIDA or Cu²⁺-DSIDA).  In this bottom-up approach, the underlying support is a poly(methyl methacrilate) (PMMA) e-beam formed, square lattice pattern of hemispheres.  This curvature pattern sorts Cu²⁺-DOIDA to the 200 nm hemispherical lattice sites of a 600 nm ´ 600 nm unit cell in L_d - L_o phase separated lipid multibilayers.  Binding of histidine-tagged green fluorescent protein (His-GFP) creates a high density array of His-GFP-bound pixels localized to the square lattice sites.  In comparison, the negative pixel pattern is created by sorting Cu²⁺-DSIDA in L_d - L_b phase separated lipid multibilayers to the flat grid between the lattice sites followed by binding to His-GFP.  Lattice defects in the His-GFP pattern lead to interesting features such as pattern circularity.  We also observe defect-free arrays of His-GFP that demonstrate perfect arrays can be formed by this method suggesting the possibility of using this approach for the localization of various active molecules to form protein, DNA, or optically active molecular arrays.