Structural changes induced by interactions between thyroid hormones and phospholipid membranes: a Raman Spectroscopy study

Abstract

Previous reports from our laboratory have shown that thyroid hormones induce changes in the fluidity and permeability of phospholipid bilayers and modify the transmembrane dipolar organization according to their iodine content. The interactions of T2, T3, and T4 with a model membrane of dilauroylphosphatidylcholine in the liquid‐crystalline phase were analyzed by confocal Raman spectroscopy. Insights into the nature of the hormone effects on the membrane properties, as well as the structural adaptations of the hormones in response to the lipid environment were derived from the spectral changes. The series of progressive iodine substituents on the ring‐β allowed us to correlate the hormone effects according to the number and the orientation of the iodine atoms. T4 was responsible for producing the highest alteration in the hydrophobic region of the membrane. Copyright © 2012 John Wiley & Sons, Ltd.

Raman spectroscopy study of the interaction of 3,5,3′‐triiodo‐L‐thyronine with phosphatidylglycerol lipid bilayers

“…Upon band decomposition, three main components centered at 1102, 1096, and 1090 cm À1 and two less intense contributors at lower wavenumbers were obtained. Taking into account that only a few isolated C-C gauche conformers are expected in the gel phase [22] and according to the behavior observed in Raman spectrum of PC membranes, [17,18] the two weak components, at 1085 and 1079 cm À1 , are assigned to ν(C-C) G of gauche conformers, located at different positions in the acyl chains. Then, the main component bands are associated to vibrations belonging to groups located in the polar region of the membrane (PO 2 À and glycerol -CH 2 OH).…”

“…This assignment is based on the consideration that the PO 2 À groups are involved in different inter and intramolecular associations. [17,18,22,45,46] Theoretical predictions concerning the conformations adopted by the isolated…”

“…[33,34] This process has been applied to decompose the complex bands in previous works. [17,18] Briefly, the number and position of components bands were obtained through deconvolutions and derivations. These, together with the band shape (a combination of Lorentzian and Gaussian functions), [35] were fixed during the first 500 iterations.…”

“…[13,14] Bilayers constituted by dilauroylphosphatidylcholine (DLPC) and dipalmitoylphosphatidylcholine (DPPC) in interaction with 3,5-diiodo-L-thyronine (T2), 3,5,3-triiodo-L-thyronine (T3), and thyroxine (T4) were previously studied by using Raman spectroscopy. [15][16][17][18] It is well known that this technique is useful to describe the changes that suffer model membranes by the action of different biomolecules. [19][20][21][22][23] Moreover, the use of a confocal microscope integrated to the Raman spectrometer improves the efficiency of this technique because Raman scattering is collected from a small volume of sample containing a relatively high local concentration of lipid and minimum contribution from the surroundings.…”

“…In addition, we were able to discriminate between the PO 2 À symmetric stretching and the C-C gauche stretching modes in the gel and the liquid crystalline phases of lipid membranes, such as in DPPC and DLPC, respectively, whose assignments had been ambiguous up to then. [17,18] Our studies focus now on lipid systems with different chemical nature, by analyzing the interactions between T3 and bilayers composed by phosphatidylglycerol lipids (PG) in both the liquidcrystalline (L α ) and the gel (L β´) phases. The main purpose of studying these systems is to inquire about the response that anionic membranes give when they interact with relatively small biomolecules.…”