Diffusion NMR study of complex formation in membrane-associated peptides

Barhoum, Suliman; Booth, Valerie; Yethiraj, Anand

doi:10.1007/s00249-013-0890-4

Cited by 7 publications

(5 citation statements)

References 53 publications

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“…The CMC of free SDS under these conditions was determined as 3.7 ± 0.3 mM by scattering measurements (S1 Fig) and 3.8 mM from DOSY measurements (Fig 5A). The diffusion coefficient of monomeric SDS is (4.6 ± 0.2) × 10 −10 m 2 s −1 , in good consistency with values ranging from 4.7 to 4.9 × 10 −10 m 2 s −1 , as published elsewhere [48]. Above the CMC, monomeric SDS is in rapid exchange with micelles and its diffusion coefficient decreased progressively with an increase in concentration.…”

Section: Resultssupporting

confidence: 89%

The influence of N-terminal acetylation on micelle-induced conformational changes and aggregation of α-Synuclein

et al. 2017

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The biological function of α-Synuclein has been related to binding to lipids and membranes but these interactions can also mediate α-Synuclein aggregation, which is associated to Parkinson’s disease and other neuropathologies. In brain tissue α-Synuclein is constitutively N-acetylated, a modification that plays an important role in its conformational propensity, lipid and membrane binding, and aggregation propensity. We studied the interactions of the lipid-mimetic SDS with N-acetylated and non-acetylated α-Synuclein, as well as their early-onset Parkinson’s disease variants A30P, E46K and A53T. At low SDS/protein ratios α-Synuclein forms oligomeric complexes with SDS micelles with relatively low α-helical structure. These micellar oligomers can efficiently nucleate aggregation of monomeric α-Synuclein, with successive formation of oligomers, protofibrils, curly fibrils and mature amyloid fibrils. N-acetylation reduces considerably the rate of aggregation of WT α-Synuclein. However, in presence of any of the early-onset Parkinson’s disease mutations the protective effect of N-acetylation against micelle-induced aggregation becomes impaired. At higher SDS/protein ratios, N-acetylation favors another conformational transition, in which a second type of α-helix-rich, non-aggregating oligomers become stabilized. Once again, the Parkinson’s disease mutations disconnect the influence of N-acetylation in promoting this transition. These results suggest a cooperative link between the N-terminus and the region of the mutations that may be important for α-Synuclein function.

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Section: Resultssupporting

confidence: 89%

The influence of N-terminal acetylation on micelle-induced conformational changes and aggregation of α-Synuclein

et al. 2017

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“…In this two-site model, the surfactant must either be in the monomeric form free solution or associated within a micelle, so that we can write p f + p m = 1. As the diffusivity of SDS micelles, D m = (6.1 ± 0.9) × 10 –11 m 2 /s, and free monomers, D f = (4.7 ± 0.08) × 10 –10 m 2 /s, have been obtained from the literature, , the fraction of free SDS can be calculated for the concentrations used here with eq and the two-state fraction relationship. The fractions are found to vary depending on the bulk SDS concentration, with p f decreasing from 0.7 to 0.3 at concentrations of 10–20 mM, respectively, well above the SDS cmc.…”

Section: Resultsmentioning

confidence: 99%

Tuning the Surface Ordering of Self-Assembled Ionic Surfactants on Semiconducting Single-Walled Carbon Nanotubes: Concentration, Tube Diameter, and Counterions

et al. 2018

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We report direct spectroscopic measurements of the macromolecular organization of ionic surfactants on the surface of semiconducting single-walled carbon nanotubes (SWCNTs) within solution-processed thin films. By using vibrational sum frequency generation (VSFG) spectroscopy, sensitive measurements of interfacial surfactant ordering were obtained as a function of surfactant concentration for sodium dodecyl sulfate (SDS)-encapsulated (6,5) and (7,6) SWCNTs with and without excess electrolytes. Anionic surfactants are known to effectively stabilize SWCNTs. The current models suggest a strong influence of the dispersion conditions on the surfactant interfacial macromolecular organization and self-assembly. Direct experimental probes of such an organization using nanotubes of specific chirality are needed to validate the existing models. We found that as the bulk SDS concentration increases near the surfactant critical micelle concentration, the interfacial ordering increased, approaching the formation of cylindrical-like micelles with the nanotube at the core. At the higher surfactant concentrations measured here, the (6,5) SWCNTs produced more ordered structures relative to those with the (7,6) SWCNTs. The relatively larger-diameter (7,6) chiral tubes support enhanced van der Waals (vdW) interactions between the tube carbon surface and the surfactant methylene chain groups that likely increase the density of gauche defects. A new effect arises when the precursor solution is exposed to a small concentration of divalent Ca counterions. We postulate that a salt-bridging configuration on such highly curved surfaces decreases the ordering of interfacial surfactant molecules, resulting in compact, disordered structures. However, this phenomenon was not observed with excess Na ions at the same ionic strength. Instead, a modest increase in surfactant ordering was observed with the excess monovalent electrolyte. These results provide new insights for thin film solution processing of vdW nanomaterials and demonstrate that VSFG is a sensitive probe of surfactant organization on nanostructures.

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“…For any given total concentration of SDS between CMC 1 and CMC 2 , the number of SDS ions forming micelles is decreased in the SWCNT suspension in comparison to the pure SDS solution because of the presence of nanotubes that shift the equilibrium distribution (see Figure 4a). Since the diffusivity of SDS micelles, D m = (6.1 ± 0.9) × 10 −11 m 2 /s, and free monomers, D f = (4.7 ± 0.08) × 10 −10 m 2 /s, are wellknown, 56 the fraction of free SDS can be calculated at low SDS concentration (10 mM) using eq 2. 36 This fraction was found to be equal to 0.77 and 0.76 ± 0.03 with and without SWCNTs, respectively.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Error bars for these measurements are about ±0.0001, which are smaller than the data points plotted. (c) Change in the concentration of free monomer and micelles as a function of the total concentration of SDS based on literature data . Note that the fractions of free monomer at 10 and 20 mM SDS are ∼0.7 and ∼0.3, respectively.…”

Section: Resultsmentioning

confidence: 99%

Strongly Bound Sodium Dodecyl Sulfate Surrounding Single-Wall Carbon Nanotubes

Xu¹,

Mueller²,

Hazelbaker³

et al. 2017

Langmuir

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NMR techniques have been widely used to infer molecular structure, including surfactant aggregation. A combination of optical spectroscopy, proton NMR spectroscopy, and pulsed field gradient NMR (PFG NMR) is used to study the adsorption number for sodium dodecyl sulfate (SDS) with single-wall carbon nanotubes (SWCNTs). Distinct transitions in the NMR chemical shift of SDS are observed in the presence of SWCNTs. These transitions demonstrate that micelle formation is delayed by SWCNTs due to the adsorption of SDS on the nanotube surface. Once the nanotube surface is saturated, the free SDS concentration increases until micelle formation is observed. Therefore, the adsorption number of SDS on SWCNTs can be determined by the changes to the apparent critical micelle concentration (CMC). PFG NMR found that SDS remains strongly bound onto the nanotube. Quantitative analysis of the diffusivity of SDS allowed calculation of the adsorption number of strongly bound SDS on SWCNTs. The adsorption numbers from these techniques give the same values within experimental error, indicating that a significant fraction of the SDS interacting with nanotubes remains strongly bound for as long as 0.5 s, which is the maximum diffusion time used in the PFG NMR measurements.

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Diffusion NMR study of complex formation in membrane-associated peptides

Cited by 7 publications

References 53 publications

The influence of N-terminal acetylation on micelle-induced conformational changes and aggregation of α-Synuclein

The influence of N-terminal acetylation on micelle-induced conformational changes and aggregation of α-Synuclein

Tuning the Surface Ordering of Self-Assembled Ionic Surfactants on Semiconducting Single-Walled Carbon Nanotubes: Concentration, Tube Diameter, and Counterions

Strongly Bound Sodium Dodecyl Sulfate Surrounding Single-Wall Carbon Nanotubes

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