Conformational aspects and rotational dynamics of synthetic adrenocorticotropin-(1-24) and glucagon in reverse micelles

Abstract

The tryptophan (Trp) rotational dynamics and the secondary structure of the peptide hormones adrenocorticotropin-(1-24) [ACTH(1-24)]--the fully active N-terminal fragment of adrenocorticotropin-(1-39)--and glucagon were studied in aqueous solutions and in reverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/water/isooctane, a system selected to mimic the membrane-water interface. In aqueous solutions, the total fluorescence intensity decays of their single Trp residue [Trp-9 and Trp-25 for ACTH(1-24) and glucagon, respectively] are multiexponential. This is also the case for ACTH(5-10), a fragment of the adrenocorticotropin "message" region. Time-resolved fluorescence anisotropy data evidence a high degree of rotational freedom of the single Trp residue. Transfer of these peptides from water to the aqueous core of reverse micelles induces severe restrictions of the Trp internal motion and of its local environment. The results indicate that the Trp-9 residue in ACTH(1-24 is maintained in the close neighborhood of the water-AOT molecular interface where the water molecules are strongly immobilized. By contrast, the Trp residues in ACTH(5-10) and glucagon are likely to be located closer to the center of the micellar aqueous core where the water molecules are in a more mobile state. Furthermore, the above location of Trp can be extended to the peptide chains themselves as evidenced by the overall correlation time values of the peptide-containing micelles. Nevertheless, in all peptides, the indole ring remains susceptible to oxidation by N-bromosuccinimide. Circular dichroism measurements evidence the induction in glucagon of alpha-helices remaining unaffected by the micellar water content. Conversely, beta-sheet structures are favored in ACTH(1-24) at low water-to-surfactant molar ratios (w0) but are disrupted by subsequent additions of water. These results are discussed in terms of the possible role of the micellar interfaces in selecting the preferred peptide dynamical conformation(s)

Conformational Flexibility of Domain III of Annexin V at Membrane/Water Interfaces

“…Reverse micelles were prepared as previously described (45). Briefly, reverse micelles of AOT and water in isooctane were prepared with 0.1 M AOT and the desired amount of water.…”

Somatostatin in a Water‐restricted Environment: Fluorescence and Circular Dichroism Study in Aot Reverse Micelles

“…Corrected emission spectra were recorded on a Hitachi F4010 spectrofluorometer, using excitation at 280 nm. Excitation and emission bandwidths of ( 5 , I S ) , (5,5 ) and (3,5 ) nm were used to measure wavelength at emission maximum and bandwidth, quantum yield and steady-state anisotropy, respectively. Peptide-free micellar solutions of appropriate wo were used as reference blanks in all absorption and emission measurements, Quantum yield of thc peptide (+, , ) in aqueous and reverse micellar solutions was determined relative to that of a solution of ~-T r p at pH 7.0 ($Trp.…”

Redox‐Controlled Fluorescence Modulation in a BODIPY‐Quinone Dyad

“…Because lipid oxidative stress is a well established cause of cell damage, [37] we were interested to test the reporting capabilities of the two redox sensors in a lipid-like environment. To mimic lipid membranes, micelles dispersed in water have been used widely, [38] seeing as they can encapsulate organic molecules in the hydrophobic core. The two compounds, BD-PQ and BD-PHQ, are totally insoluble in water.…”