Synthetic Approaches to Functionalized Lipids for Protein Monolayer Crystallizations

Abstract

The use of lipid monolayers to bind and adsorb proteins is an attractive and increasingly important method for generating high localized concentrations of oriented proteins and protein complexes. These bound proteins can be imaged directly, or they may form 2-D crystalline arrays that are amenable to structure determination by single particle analysis or 2-D electron crystallography. 2-D crystals grown by this technique can also be used to initiate the growth of 3-D crystals for X-ray diffraction analysis. Many derivatized lipids have been prepared for use with this technique, incorporating a diverse range of ligands to enable binding to specific proteins. Synthetic lipids containing functionalized head groups that chelate Ni 2+ or Cu 2+ have also been prepared to bind and orient expressed proteins that contain His-tags. Protein-binding monolayer-forming lipids generally consist of two distinct components: (1) a branched hydrocarbon tail to confer fluidity to the monolayer and (2) a functionalized hydrophilic head group to facilitate binding of protein molecules at the air-water interface. Newer examples of these compounds also incorporate perfluorinated hydrocarbon moieties to confer detergent resistance to these lipids. This review focuses on synthetic approaches to functionalized lipids for protein monolayer crystallizations.

Functionalization of cobalt porphyrin–phospholipid bilayers with his-tagged ligands and antigens

“… 15 , 16 Ni-NTA conjugated phospholipids, which were described over 20 years ago and are commercially available, have also been used to bind his-tagged proteins, but largely in the context of structural biology studies. 17 – 19 Unfortunately, the chelation of his-tagged proteins with various Ni-NTA lipids in nanoparticulate form is not stable in biological media such as serum. 20 , 21 Based on the suitability of lipids for use in vivo in the form of liposomes or as coatings for other nanoparticles 22 , stable lipid-based polyhistidine-binding would be enabling for applications in biological settings.…”

Molecular Packing of Functionalized Fluorinated Lipids in Langmuir Monolayers

“…Single-chain fluorinated surfactants hold promise for a number of exciting applications including the stabilization of membrane proteins for in vitro studies, either during cell-free expression or following membrane extraction. Fluorinated surfactants substituted for standard detergents have, for example, been shown to reduce denaturation and dissociation of detergent-sensitive proteins and protein complexes. − Liposome-forming fluorinated lipids, which exhibit reduced permeability, enhanced stability, and enhanced resistance to disruptive biocompounds and bile salts, have been used in the development of new intravenous drug and gene delivery systems. , More recently, monolayer-forming fluorinated lipids have found use in the 2D crystallization of hydrophobic or partially hydrophobic proteins at the air−water interface …”

Comparison of Fluorinated and Nonfluorinated Lipids in Self-Adjuvanting Delivery Systems for Peptide-Based Vaccines

“…Multiple delivery systems have been reported to deliver peptide epitopes to the APCs, including lipopeptides, polymers, virus-like particles, and liposomes. , However, fluorinated amphiphiles have not yet been examined for this purpose. These compounds have biomedical applications as components of liposomal drug carriers, for ultrasound-mediated delivery of lipophilic drugs or for two-dimensional crystallization of histidine (His)-tagged membrane protein. − Fluorinated amphiphiles can form a third phase that is immiscible with aqueous and nonaqueous phases and thus self-assemble into nanoparticles . They also do not accumulate in lipid membranes .…”