A bola-phospholipid bearing tetrafluorophenylazido chromophore as a promising lipid probe for biomembrane photolabeling studies

Synthesis of a photocleavable bola-phosphatidylcholine

Phosphatidylinositol transfer proteins (PITPs) are ubiquitous in eukaryotes and are involved in the regulation of phospholipid metabolism, membrane trafficking, and signal transduction. Sec14 is a yeast PITP that has been shown to transfer phosphatidylinositol (PI) or phosphatidylcholine (PC) from the endoplasmic reticulum to the Golgi. It is now believed that Sec14 may play a greater role than just shuttling PI and PC throughout the cell. Genetic evidence suggests that retrieval of membrane-bound PI by Sec14 also manages to present PI to the phosphatidylinositol-4-kinase, Pik1, to generate phosphatidylinositol-4-phosphate, PI(4)P. To test this hypothetical model, we designed a photocleavable bolalipid to span the entire membrane, having one phosphatidylcholine or phosphatidylinositol headgroup on each leaflet connected by a photocleavable diacid. Sec14 should not be able to present the bola-PI to Pik1 for phosphorylation as the head group will be difficult to lift from the bilayer as it is tethered on the opposite leaflet. After photocleavage the two halves would behave as a normal phospholipid, thus phosphorylation by Pik1 would resume. We report here the synthesis of a photocleavable bola-PC, a precursor to the desired bola-PI. The mono-photocleavable bola-PC lipid was designed to contain two glycerol molecules with choline head groups connected through a phosphodiester bond at the sn3 position. Each glycerol was acylated with palmitic acid at the sn1 position. These two glycerol moieties were then connected through their respective sn2 hydroxyls via a photocleavable dicarboxylic acid containing a nitrophenyl ethyl photolabile protecting group. The bola-PC and its precursors were found to undergo efficient photocleavage when irradiated in solution or in vesicles with 365 nm light for two minutes. Treatment of the bola-PC with a mutant phospholipase D and myo-inositol produced a mono-inositol bola-PC-PI.

The Application of Fluorine-Containing Reagents in Structural Proteomics

Structural proteomics refers to large-scale mapping of protein structures in order to understand the relationship between protein sequence, structure, and function. Chemical labeling, in combination with mass-spectrometry (MS) analysis, have emerged as powerful tools to enable a broad range of biological applications in structural proteomics. The key to success is a biocompatible reagent that modifies a protein without affecting its high-order structure. Fluorine, well-known to exert profound effects on the physical and chemical properties of reagents, should have an impact on structural proteomics. In this Minireview, we describe several fluorine-containing reagents that can be applied in structural proteomics. We organize their applications around four MS-based techniques: a) affinity labeling, b) activity-based protein profiling (ABPP), c) protein footprinting, and d) protein cross-linking. Our aim is to provide an overview of the research, development, and application of fluorine-containing reagents in protein structural studies.

Deuterium- and Tritium-Labelled Compounds: Applications in the Life Sciences

Hydrogen isotopes are unique tools for identifying and understanding biological and chemical processes. Hydrogen isotope labelling allows for the traceless and direct incorporation of an additional mass or radioactive tag into an organic molecule with almost no changes in its chemical structure, physical properties, or biological activity. Using deuterium-labelled isotopologues to study the unique mass-spectrometric patterns generated from mixtures of biologically relevant molecules drastically simplifies analysis. Such methods are now providing unprecedented levels of insight in a wide and continuously growing range of applications in the life sciences and beyond. Tritium (³ H), in particular, has seen an increase in utilization, especially in pharmaceutical drug discovery. The efforts and costs associated with the synthesis of labelled compounds are more than compensated for by the enhanced molecular sensitivity during analysis and the high reliability of the data obtained. In this Review, advances in the application of hydrogen isotopes in the life sciences are described.

Croix CM, Tyurina YY, Planas-Iglesias J, Jiang J, Huang Z, Amoscato AA, Tyurin VA, Kapralov AA, Cheikhi A, Maguire J, Klein-Seetharaman J, Bayır H, Kagan VE. Mitochondrial Redox Opto-Lipidomics Reveals Mono-Oxygenated Cardiolipins as Pro-Apoptotic Death Signals

While opto-genetics has proven to have tremendous value in revealing the functions of the macromolecular machinery in cells, it is not amenable to exploration of small molecules such as phospholipids (PLs). Here, we describe a redox opto-lipidomics approach based on a combination of high affinity light-sensitive ligands to specific PLs in mitochondria with LC-MS based redox lipidomics/bioinformatics analysis for the characterization of pro-apoptotic lipid signals. We identified the formation of mono-oxygenated derivatives of C18:2-containing cardiolipins (CLs) in mitochondria after the exposure of 10-nonylacridine orange bromide (NAO)-loaded cells to light. We ascertained that these signals emerge as an immediate opto-lipidomics response, but they decay long before the commencement of apoptotic cell death. We found that a protonophoric uncoupler caused depolarization of mitochondria and prevented the mitochondrial accumulation of NAO, inhibited the formation of C18:2-CL oxidation product,s and protected cells from death. Redox opto-lipidomics extends the power of opto-biologic protocols to studies of small PL molecules resilient to opto-genetic manipulations.