Energetics and Population of Molecules at Microscopic Liquid and Solid Surfaces

Wang, Hongfei; Yan, Elsa C. Y.; Liu, Yan; Eisenthal, Kenneth B.

doi:10.1021/jp980491y

Cited by 109 publications

(194 citation statements)

References 18 publications

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“…Including possible depletion of the bulk TAT population due to adsorption by the liposome surface yields a modified Langmuir equation given by ref. 40,…”

Section: Resultsmentioning

confidence: 99%

Label-free probe of HIV-1 TAT peptide binding to mimetic membranes

Rao

Kwok

Lombardi

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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The transacting activator of transduction (TAT) protein plays a key role in the progression of AIDS. Studies have shown that a +8 charged sequence of amino acids in the protein, called the TAT peptide, enables the TAT protein to penetrate cell membranes. To probe mechanisms of binding and translocation of the TAT peptide into the cell, investigators have used phospholipid liposomes as cell membrane mimics. We have used the method of surface potential sensitive second harmonic generation (SHG), which is a label-free and interface-selective method, to study the binding of TAT to anionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-1′-rac-glycerol (POPG) and neutral 1-palmitoyl-2-oleoylsn-glycero-3-phosphocholine (POPC) liposomes. It is the SHG sensitivity to the electrostatic field generated by a charged interface that enabled us to obtain the interfacial electrostatic potential. SHG together with the Poisson-Boltzmann equation yielded the dependence of the surface potential on the density of adsorbed TAT. We obtained the dissociation constants K d for TAT binding to POPC and POPG liposomes and the maximum number of TATs that can bind to a given liposome surface. For POPC K d was found to be 7.5 ± 2 μM, and for POPG K d was 29.0 ± 4.0 μM. As TAT was added to the liposome solution the POPC surface potential changed from 0 mV to +37 mV, and for POPG it changed from −57 mV to −37 mV. A numerical calculation of K d , which included all terms obtained from application of the Poisson-Boltzmann equation to the TAT liposome SHG data, was shown to be in good agreement with an approximated solution.Gouy-Chapman model | hyper-Rayleigh scattering | biomolecules/water interface | colloid/water interface | nonlinear optical spectroscopy T he HIV type 1 (HIV-1) transacting activator of transduction (TAT) is an important regulatory protein for viral gene expression (1-3). It has been established that the TAT protein has a key role in the progression of AIDS and is a potential target for anti-HIV vaccines (4). For the TAT protein to carry out its biological functions, it needs to be readily imported into the cell. Studies on the cellular internalization of TAT have led to the discovery of the TAT peptide, a highly cationic 11-aa region (protein transduction domain) of the 86-aa full-length protein that is responsible for the TAT protein translocating across phospholipid membranes (5-8). The TAT peptide is a member of a class of peptides called cell-penetrating peptides (CPPs) that have generated great interest for drug delivery applications (ref. 9 and references therein). The exact mechanism by which the TAT peptide enters cells is not fully understood, but it is likely to involve a combination of energy-independent penetration and endocytosis pathways (8, 10). The first step in the process is high-affinity binding of the peptide to phospholipids and other components on the cell surface such as proteins and glycosaminoglycans (1, 9).The binding of the TAT peptide to liposomes has been investigated using a variety of techniques, each...

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“…Including possible depletion of the bulk TAT population due to adsorption by the liposome surface yields a modified Langmuir equation given by ref. 40,…”

Section: Resultsmentioning

confidence: 99%

Label-free probe of HIV-1 TAT peptide binding to mimetic membranes

Rao

Kwok

Lombardi

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

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“…Therefore, SHG can be generated from this kind of material provided the size of the microparticle is comparable to the coherence length of the SHG, i.e., roughly the wavelength of the SH light. [22][23][24][25][26][27][28][29][30][31][32][33] One of the promising applications of this method is to investigate transport kinetics of molecules across liposome bilayers. 28,31,33 Liposomes are spherical self-assembled bilayer structures that separate two aqueous phases.…”

Section: Methodsmentioning

confidence: 99%

Effects of Counterions on Molecular Transport Across Liposome Bilayer: Probed by Second Harmonic Generation

et al. 2001

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The transport rate of an organic cation, malachite green (MG), across a unilamellar bilayer (∼105 nm) of the dioleoylphosphatidylglycerol (DOPG) liposome has been studied by the SHG technique. This is the first time to our knowledge that the effects of anions on molecular cation transport have been observed. Our studies show four results. First, in the presence of sodium chloride (NaCl) or sodium bromide (NaBr), the time constant for transport of MG across the DOPG bilayer increases with the increase in the concentration of the counterion (i.e., Cl -or Br -). Second, with the organic electrolytes, sodium citrate (NaCitrate) and sodium ethanesulfonate (NaEtSO 3 ), the transport rate is independent of the concentration of the counterion (i.e., Citrateand EtSO 3 -). Third, at the same counterion concentration, the transport rate depends on the species of the counterion used. The rate of MG transport is the slowest with Cl -, faster with Br -, and the fastest with the two organic counterions, Citrate -and EtSO 3 -. Last, at the low counterion concentration of 1mM, the transport rates of MG were found to approach the same value for the four anions. A brief discussion of a possible mechanism is presented.

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“…Since the SHS amplitude increases with the number of adsorbed molecules an isotherm can be produced. With such measurements it is possible to determine the Gibbs adsorption energy, [61] or to get access to the adsorption model. [62,63] Much of this work has been reviewed by Eisenthal.…”

Section: Electrostatically Stabilized Systemsmentioning

confidence: 99%

Nonlinear Optical Spectroscopy of Soft Matter Interfaces

Roke

2009

ChemPhysChem

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Molecular interfacial properties of colloidal soft matter systems (for example vesicle fusion, or particle synthesis) can be investigated without the need of planar model systems or fluorescent labelling. Exclusively observing chemical properties and changes in a molecular layer of a few molecular dimensions thick around a small particle adds a new dimension to the field of surface science (see figure). Soft matter consists of complex molecules that can undergo drastic structural transformations under mild changes of chemical and physical conditions. Since a wide variety of chemical, physical and biological processes occur at soft matter interfaces, they can exhibit complex behavior. This is even more so for interfaces of colloidal soft matter since the relative amount of interface material increases by orders of magnitude. Herein, we focus on new developments that enable us to obtain detailed molecular structural changes in the topmost molecular layers of soft matter interfaces composed of complex bio‐molecules. In particular, the possibilities to probe interfaces of colloidal soft matter systems are discussed.

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Energetics and Population of Molecules at Microscopic Liquid and Solid Surfaces

Cited by 109 publications

References 18 publications

Label-free probe of HIV-1 TAT peptide binding to mimetic membranes

Label-free probe of HIV-1 TAT peptide binding to mimetic membranes

Effects of Counterions on Molecular Transport Across Liposome Bilayer: Probed by Second Harmonic Generation

Nonlinear Optical Spectroscopy of Soft Matter Interfaces

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