Psychoactive Plant Database - Neuroactive Phytochemical Collection

1. Biointerphases. 2013 Dec;8(1):1. doi: 10.1186/1559-4106-8-1. Epub 2013 Jan 17.

Fluorescence modulation sensing of positively and negatively charged proteins on 
lipid bilayers.

Robison AD(1), Huang D, Jung H, Cremer PS.

Author information:
(1)Department of Chemistry, Texas A&M University, 3255 TAMU, College Station, 
TX, 77843, USA, arobison@mail.chem.tamu.edu.

BACKGROUND: Detecting ligand-receptor binding on cell membrane surfaces is 
required to understand their function and behavior. Detection platforms can also 
provide an avenue for the development of medical devices and sensor 
biotechnology. The use of fluorescence techniques for such purposes is highly 
desirable as they provide high sensitivity. Herein, we describe a technique that 
utilizes the sensitivity of fluorescence without directly tagging the analyte of 
interest to monitor ligand-receptor interactions on supported lipid bilayers. 
The fluorescence signal is modulated according to the charge state of the target 
analyte. The binding event elicits protonation or deprotonation of pH-responsive 
reporter dyes embedded in the lipid bilayer.
METHODS: Supported lipid membranes containing ortho-conjugated rhodamine B-POPE 
(1-hexadecanoyl-2-(9Z-octadecenoyl)-sn-glycero-3-phosphoethanolamine), which 
fluoresces in its protonated but not in its deprotonated form, were utilized as 
sensor platforms for biotin-avidin and biotin-streptavidin binding events. The 
membranes contained 5 mol% biotin-PE 
(1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-(cap biotinyl) (sodium salt) 
as a capture ligand. Supported lipid bilayers were formed in the channels of 
microfluidic devices and the fluorescence intensity of the dye was monitored as 
protein was introduced.
RESULTS: The binding of avidin, which is positively charged at pH 7.2, made the 
bilayer surface charge more positive, which in turn deprotonated the 
ortho-rhodamine B dye, reducing its fluorescence. The binding of streptavidin, 
which is negatively charged at pH 7.2, had the opposite effect. Reducing the 
ionic strength of the analyte solution by removing 150 mM NaCl from the 10 mM 
phosphate buffered saline (PBS) solution raised the apparent pKa of the 
ortho-rhodamine B titration point by about 1 pH unit. This could be exploited in 
conjunction with bulk solution pH changes to turn the rhodamine B-POPE dye into 
a sensor for streptavidin involving a decrease, rather than an increase, in the 
fluorescence response, at pH values below streptavidin's pI value.
CONCLUSIONS: This study demonstrates the ability to monitor ligand-receptor 
interactions on supported lipid bilayers through the protonation or 
deprotonation of reporter dyes for both negatively and positively charged 
analytes over a range of pH and ionic strength conditions. Specifically, the 
sensitivity and pH-operating range of this technique can be optimized by 
modulating the sensing conditions which are employed.

DOI: 10.1186/1559-4106-8-1
PMID: 24706114 [Indexed for MEDLINE]


2. Langmuir. 2013 Dec 3;29(48):15022-31. doi: 10.1021/la4036453. Epub 2013 Nov
21.

Lipid compositions modulate fluidity and stability of bilayers: characterization 
by surface pressure and sum frequency generation spectroscopy.

Liu W(1), Wang Z, Fu L, Leblanc RM, Yan EC.

Author information:
(1)Department of Chemistry, Yale University , 225 Prospect Street, New Haven, 
Connecticut 06520, United States.

Cell membranes are crucial to many biological processes. Because of their 
complexity, however, lipid bilayers are often used as model systems. Lipid 
structures influence the physical properties of bilayers, but their interplay, 
especially in multiple-component lipid bilayers, has not been fully explored. 
Here, we used the Langmuir-Blodgett method to make mono- and bilayers of 
1,2-dihexadecanoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG), 
1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (POPG), and 
1-hexadecanoyl-2-(9Z-octadecenoyl)-sn-glycero-3-phospho-L-serine (POPS) as well 
as their 1:1 binary mixtures. We studied the fluidity, stability, and rigidity 
of these structures using sum frequency generation (SFG) spectroscopy combined 
with analyses of surface pressure-area isotherms, compression modulus, and 
stability. Our results show that single-component bilayers, both saturated and 
unsaturated, may not be ideal membrane mimics because of their low fluidity 
and/or stability. However, the binary saturated and unsaturated DPPG/POPG and 
DPPG/POPS systems show not only high stability and fluidity but also high 
resistance to changes in surface pressure, especially in the range of 25-35 
mN/m, the range typical of cell membranes. Because the ratio of saturated to 
unsaturated lipids is highly regulated in cells, our results underline the 
possibility of modulating biological properties using lipid compositions. Also, 
our use of flat optical windows as solid substrates in SFG experiments should 
make the SFG method more compatible with other techniques, enabling more 
comprehensive future surface characterizations of bilayers.

DOI: 10.1021/la4036453
PMID: 24245525 [Indexed for MEDLINE]


3. Biochim Biophys Acta. 2013 Sep;1828(9):2204-14. doi: 
10.1016/j.bbamem.2013.05.020. Epub 2013 Jun 7.

Phase diagram of a 4-component lipid mixture: DSPC/DOPC/POPC/chol.

Konyakhina TM(1), Wu J, Mastroianni JD, Heberle FA, Feigenson GW.

Author information:
(1)Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 
14853, USA.

We report the first 4-component phase diagram for the lipid bilayer mixture, 
DSPC/DOPC/POPC/chol 
(distearoylphosphatidylcholine/dioleoylphosphatidylcholine/1-palmitoyl, 
2-oleoylphosphatidylcholine/cholesterol). This phase diagram, which has 
macroscopic Ld+Lo phase domains, clearly shows that all phase boundaries 
determined for the 3-component mixture containing DOPC transition smoothly into 
the boundaries for the 3-component mixture containing POPC, which has nanoscopic 
phase domains of Ld+Lo. Our studies start from two published ternary phase 
diagrams, and show how these can be combined into a quaternary phase diagram by 
study of a few hundred samples of intermediate compositions.

Copyright © 2013 Elsevier B.V. All rights reserved.

DOI: 10.1016/j.bbamem.2013.05.020
PMCID: PMC3738200
PMID: 23747294 [Indexed for MEDLINE]


4. Biophys Chem. 2010 Mar;147(1-2):20-7. doi: 10.1016/j.bpc.2009.12.005. Epub
2009  Dec 24.

Properties of phosphatidylcholine in the presence of its monofluorinated 
analogue.

Smith EA(1), van Gorkum CM, Dea PK.

Author information:
(1)Department of Chemistry, Occidental College, 1600 Campus Road, Los Angeles, 
CA 90041, USA.

In aqueous solution, the monofluorinated phospholipid 
1-palmitoyl-2-[16-fluoropalmitoyl]sn-glycero-3-phosphocholine (F-DPPC) 
interdigitates without the use of inducing agents. To understand the thermal and 
physical properties of this unique lipid, F-DPPC was combined with the 
non-fluorinated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and 
1,2-diarachidoyl-sn-glycero-3-phosphocholine (DAPC). Differential scanning 
calorimetry (DSC) was used to determine the miscibility and thermotropic phase 
behavior of these binary lipid mixtures. In addition, the fluorescent probe 
1,6-diphenyl-1,3,5-hexatriene (DPH) and a DPH-labeled analogue of DPPC, 
2-(3-(diphenylhexatrienyl) propanoyl)-1-hexadecanoyl-sn-glycero-3-phosphocholine 
(beta-DPH HPC, aka DPH-PC or DPHpPC), were used to detect interdigitation. In 
F-DPPC, the fluorescence intensity of both probes decreased a similar amount and 
to a degree that is consistent with an interdigitated system. We also determined 
that there are two separate effects of increasing the ratio of F-DPPC in the 
DPPC/F-DPPC system. With low amounts of F-DPPC, there is little evidence that 
the system is heavily interdigitated. Instead, we hypothesize that the 
introduction of F-DPPC provides nucleation sites that alter the kinetics, 
reversibility, and temperature of the main transition (T(m)). At higher mol% of 
F-DPPC, we propose that interdigitated F-DPPC-rich domains form to create a 
phase-segregated system. While DPPC/F-DPPC was highly miscible, the DAPC/F-DPPC 
system was significantly less miscible. Additionally, we observed that 
DAPC/F-DPPC samples have reduced solubility in water, which affected the 
acquisition of fluorescence data. However, our DSC results indicate the 
existence of DAPC-rich and F-DPPC-rich components. Furthermore, this data 
support that the mixing was disruptive to lipid packing and that the presence of 
DAPC hinders the interdigitation of F-DPPC.

Copyright 2009 Elsevier B.V. All rights reserved.

DOI: 10.1016/j.bpc.2009.12.005
PMID: 20064684 [Indexed for MEDLINE]


5. J Fluoresc. 2008 Mar;18(2):555-62. doi: 10.1007/s10895-007-0299-5. Epub 2007
Dec  23.

Characterization of monoolein-based lipoplexes using fluorescence spectroscopy.

Neves Silva JP(1), Coutinho PJ, Real Oliveira ME.

Author information:
(1)Physics Department, University of Minho, Campus of Gualtar, Braga, Portugal.

Lipoplexes are commonly used as delivery systems in vitro and in vivo, the role 
of a neutral lipid as helper being of extreme importance in these systems. 
Cationic liposomes composed of dioctadecyldimethylammonium bromide (DODAB) with 
monoolein (MO) as a helper, at different molar ratios (1:2; 1:1 and 1:0.5) were 
prepared, and subsequently titrated to DNA. The structural and physicochemical 
properties of the lipid/DNA complexes were assessed by ethidium bromide (EtBr) 
exclusion, 90 degrees static light scattering (90 degrees SLS) assays and 
fluorescence resonance energy transfer (FRET). In EtBr exclusion assays, the 
steady-state fluorescence spectra of EtBr were decomposed into the sum of two 
lognormal emissions, emanating from two different environments--H(2)O and DNA, 
and the effect of charge ratio (+/-) was observed. 90 degrees SLS assays gave an 
important contribution, detecting size variations in systems with different MO 
fractions on the lipoplexes. In FRET assays, 
2-(3-(diphenylhexatrienyl)propanoyl)-1-hexadecanoyl-sn-glycero-3-phosphocholine 
(DPH-HPC) was used as donor and EtBr as acceptor. The DNA component previously 
calculated by EtBr exclusion, was used to determine the energy transfer 
efficiency, as an indirect measurement of the lipoplexes structural and 
physicochemical properties. Our results demonstrate that the inclusion of 
monoolein in the cationic liposomes formulation significantly modifies the rate 
of DNA complexation, being DODAB:MO (1:1) the system with higher DNA 
condensation efficiency.

DOI: 10.1007/s10895-007-0299-5
PMID: 18157688 [Indexed for MEDLINE]