Monitoring Phosphatidic Acid Formation in Intact Phosphatidylcholine Bilayers upon Phospholipase D Catalysis

We have monitored the production of the negatively charged lipid, 1-palmitoyl-2-oleoyl-<i>sn</i>-glycero-3-phosphatidic acid acid (POPA), in supported lipid bilayers via the enzymatic hydrolysis of 1-palmitoyl-2-oleoyl-<i>sn</i>-glycero-3-phosphocholine (PC), a zwitterionic lipid. Experiments were performed with phospholipase D (PLD) in a Ca²⁺ dependent fashion. The strategy for doing this involved using membrane-bound streptavidin as a biomarker for the charge on the membrane. The focusing position of streptavidin in electrophoretic-electroosmotic focusing (EEF) experiments was monitored via a fluorescent tag on this protein. The negative charge increased during these experiments due to the formation of POPA lipids. This caused the focusing position of streptavidin to migrate toward the negatively charged electrode. With the use of a calibration curve, the amount of POPA generated during this assay could be read out from the intact membrane, an objective that has been otherwise difficult to achieve because of the lack of unique chromophores on PA lipids. On the basis of these results, other enzymatic reactions involving the change in membrane charge could also be monitored in a similar way. This would include phosphorylation, dephosphorylation, lipid biosynthesis, and additional phospholipase reactions

Deflected Capillary Force Lithography

Herein we introduce a novel strategy based on capillary force lithography (CFL) to fabricate asymmetric polymeric ring structures by applying both shear and nomal forces to a poly(dimethylsiloxane) stamp. The mechanism for the formation of asymmetric rings is caused by the deflection of cylindrical PDMS pillars due to the shear load, which is therefore termed deflected CFL (dCFL). The asymmetric polymeric rings could be readily transferred to an underlying gold layer to generate split ring structures with tunable opening angles. Asymmetric structures based upon trigular and square-shaped pillars were also fabricated. These elements were formed into periodic arrays over surface areas as large as 1 cm² and may have optical and electromagnetic applications

Sensing Small Molecule Interactions with Lipid Membranes by Local pH Modulation

Herein, we utilized a label-free sensing platform based on pH modulation to detect the interactions between tetracaine, a positively charged small molecule used as a local anesthetic, and planar supported lipid bilayers (SLBs). The SLBs were patterned inside a flow cell, allowing for various concentrations of tetracaine to be introduced over the surface in a buffer solution. Studies with membranes containing POPC (1-palmitoyl-2-oleoyl-<i>sn</i>-glycero-3-phosphocholine) yielded an equilibrium dissociation constant value of <i>K</i>_d = 180 ± 47 μm for this small molecule–membrane interaction. Adding cholesterol to the SLBs decreased the affinity between tetracaine and the bilayers, while this interaction tightened when POPE (1-hexadecanoyl-2-(9-<i>Z</i>-octadecenoyl)-<i>sn</i>-glycero-3-phospho­ethanolamine) was added. Studies were also conducted with three negatively charged membrane lipids, POPG (1-palmitoyl-2-oleoyl-<i>sn</i>-glycero-3-phospho-(1′-<i>rac</i>-glycerol) (sodium salt)), POPS (1-palmitoyl-2-oleoyl-<i>sn</i>-glycero-3-phospho-l-serine (sodium salt)), and ganglioside GM1. All three measurements gave rise to a similar tightening of the apparent <i>K</i>_d value compared with pure POPC membranes. The lack of chemical specificity with the identity of the negatively charged lipid indicated that the tightening was largely electrostatic. Through a direct comparison with ITC measurements, it was found that the pH modulation sensor platform offers a facile, inexpensive, highly sensitive, and rapid method for the detection of interactions between putative drug candidates and lipid bilayers. As such, this technique may potentially be exploited as a screen for drug development and analysis

Supported Lipid Bilayers with Phosphatidylethanolamine as the Major Component

Phosphatidylethanolamine (PE) is notoriously difficult to incorporate into model membrane systems, such as fluid supported lipid bilayers (SLBs), at high concentrations because of its intrinsic negative curvature. Using fluorescence-based techniques, we demonstrate that having fewer sites of unsaturation in the lipid tails leads to high-quality SLBs because these lipids help to minimize the curvature. Moreover, shorter saturated chains can help maintain the membranes in the fluid phase. Using these two guidelines, we find that up to 70 mol % PE can be incorporated into SLBs at room temperature and up to 90 mol % PE can be incorporated at 37 °C. Curiously, conditions under which three-dimensional tubules project outward from the planar surface as well as conditions under which domain formation occurs can be found. We have employed these model membrane systems to explore the ability of Ni²⁺ to bind to PE. It was found that this transition metal ion binds 1000-fold tighter to PE than to phosphatidylcholine lipids. In the future, this platform could be exploited to monitor the binding of other transition metal ions or the binding of antimicrobial peptides. It could also be employed to explore the physical properties of PE-containing membranes, such as phase domain behavior and intermolecular hydrogen bonding

Palaeoecological insights into the Changhsingian–Induan (latest Permian–earliest Triassic) bivalve fauna at Dongpan, southern Guangxi, South China

<div><p>Yang, T.L., He, W.H., Zhang, K.X., Wu, S.B., Zhang, Y., Yue, M.L., Wu, H.T. & Xiao, Y.F., XX.XXXX.2015. Palaeoecological insights into the Changhsingian–Induan (latest Permian–earliest Triassic) bivalve fauna at Dongpan, southern Guangxi, South China. <i>Alcheringa 40</i>, xxx–xxx. ISSN 0311-5518.</p><p>The Talung Formation (latest Permian) and basal part of Luolou Formation (earliest Triassic) of the Dongpan section have yielded 30 bivalve species in 17 genera. Eight genera incorporating 11 species are systematically described herein, including three new species: <i>Nuculopsis guangxiensis</i>, <i>Parallelodon changhsingensis</i> and <i>Palaeolima fangi</i>. Two assemblages are recognized, i.e., the <i>Hunanopecten exilis</i>–<i>Euchondria fusuiensis</i> assemblage from the Talung Formation and the <i>Claraia dieneri–Claraia griesbachi</i> assemblage from the Luolou Formation. The former is characterized by abundant <i>Euchondria fusuiensis</i>, an endemic species, associated with other common genera, such as <i>Hunanopecten</i>, which make it unique from coeval assemblages of South China. A palaeoecological analysis indicates that the Changhsingian bivalve assemblage at Dongpan is diverse and represented by various life habits characteristic of a complex ecosystem. This also suggests that redox conditions were oxic to suboxic in deep marine environments of the southernmost Yangtze Basin during the late Changhsingian, although several episodes of anoxic perturbations and declines in palaeoproductivity saw deterioratation of local habitats and altered the taxonomic composition or population size of the bivalve fauna.</p><p><i>Tinglu Yang [</i><a href="mailto:[email protected]" target="_blank">[email protected]</a><i>], School of Earth Sciences, China University of Geosciences, 388 Lumo Road, Hongshan, Wuhan 430074, PR China; Weihong He* [</i><a href="mailto:[email protected]" target="_blank">[email protected]</a><i>] and Kexin Zhang [</i><a href="mailto:[email protected]" target="_blank">[email protected]</a><i>], State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences, 388 Lumo Road, Hongshan, Wuhan 430074, PR China; Shunbao Wu [</i><a href="mailto:[email protected]" target="_blank">[email protected]</a><i>], Yang Zhang [</i><a href="mailto:[email protected]" target="_blank">[email protected]</a><i>], Mingliang Yue [</i><a href="mailto:[email protected]" target="_blank">[email protected]</a><i>], Huiting Wu [</i><a href="mailto:[email protected]" target="_blank">[email protected]</a><i>] and Yifan Xiao [</i><a href="mailto:[email protected]" target="_blank">[email protected]</a><i>], School of Earth Sciences, China University of Geosciences, 388 Lumo Road, Hongshan, Wuhan 430074, PR China.</i></p></div

Supported Lipid Bilayers with Phosphatidylethanolamine as the Major Component

Phosphatidylethanolamine (PE) is notoriously difficult to incorporate into model membrane systems, such as fluid supported lipid bilayers (SLBs), at high concentrations because of its intrinsic negative curvature. Using fluorescence-based techniques, we demonstrate that having fewer sites of unsaturation in the lipid tails leads to high-quality SLBs because these lipids help to minimize the curvature. Moreover, shorter saturated chains can help maintain the membranes in the fluid phase. Using these two guidelines, we find that up to 70 mol % PE can be incorporated into SLBs at room temperature and up to 90 mol % PE can be incorporated at 37 °C. Curiously, conditions under which three-dimensional tubules project outward from the planar surface as well as conditions under which domain formation occurs can be found. We have employed these model membrane systems to explore the ability of Ni²⁺ to bind to PE. It was found that this transition metal ion binds 1000-fold tighter to PE than to phosphatidylcholine lipids. In the future, this platform could be exploited to monitor the binding of other transition metal ions or the binding of antimicrobial peptides. It could also be employed to explore the physical properties of PE-containing membranes, such as phase domain behavior and intermolecular hydrogen bonding