Disorder-to-Order Markers of a Cyclic Hexapeptide Inspired from the Binding Site of Fertilin β Involved in Fertilization Process

Abstract

Synthetic peptides mimicking the binding site of fertilin β to its receptor, integrin α6β1, were shown to inhibit sperm–egg fusion when added to in vitro media. In contrast, the synthetic cyclic hexapeptide, cyclo(Cys1-Ser2-Phe3-Glu4-Glu5-Cys6), named as cFEE, proved to stimulate gamete fusion. Owing to its biological specificity, this hexapeptide could help improve the in vitro fertilization pregnancy rate in human. In an attempt to establish the structure–activity relationship of cFEE, its structural dynamics was herein analyzed by means of ultraviolet circular dichroism (UV-CD) and Raman scattering. The low concentration CD profile in water, containing mainly a deep minimum at ∼202 nm, is consistent with a rather unordered chain. However, an ordering trend of the peptide loop has been observed in a less polar solvent such as methanol, where the UV-CD signal shape is formed by a double negative marker at ∼202/215 nm, indicating the presence of a type-II′ β-turn. Raman spectra recorded in aqueous samples upon a 100-fold concentration increase, still showed an important population (∼30%) of the disordered structure. The structural flexibility of the disulfide bridge was confirmed by the Raman markers arising from the Cys1-Cys6 disulfide bond-stretch motions. Density functional theory calculations highlighted the formation of the type-II′ β-turn on the four central residues of cFEE (i.e., -Ser2-Phe3-Glu4-Glu5-) either with a left- or with a right-handed disulfide. The structure with a left-handed S–S bond, however, appears to be more stable.

Surface enhanced Raman spectroscopy based analysis of SARS-CoV-2 spike protein binding to ACE2 receptor

“…After normalization of the spectra, the features from ACE2 show a more intense amide III band and on the side of the spike protein the amide I band is more intense. In the amide III band the maximum of the first principal component is around 1300 cm -1 which can be assigned to signals from a helical structure [26,29] and in the amide I band a maximum is around 1628 cm -1 which can be assigned to the β-sheet structure [25][26][27][28]. Consequently, in this case again, the features of ACE2 show more features from the helical structure and the features from the spike protein display more a sheet structure.…”

“…Here the secondary structure can be studied by analyzing the amide I band from 1600 cm -1 to 1750 cm -1 and the amide III band within the area of 1200 cm -1 to 1380 cm -1 . Here signals can be assigned to α-helical and β-sheet structures, but also to random and β-turn structures [25][26][27][28]. In the following the samples are compared by determining relative differences in the α-helical and β-sheet structure.…”

“…In figure 3 the deconvolved signals in the amide I and amide III band of ACE2 are shown. The amide I band signals which can be assigned to a β-sheet can be located around 1635 cm -1 and 1670 cm -1 [25][26][27][28]. Signals from the α-helix can be found around 1657cm -1 and unordered or β-turn structures show signals within the range 1660 cm -1 to 1700 cm -1 [24][25][26][27].…”

Aspartate: An interesting model for analyzing dipole‐ion and ion pair interactions through its oppositely charged amine and acid groups

“…Aqueous solution behavior of an organic molecule, such as an AA or a peptide, is theoretically treated by two complementary static and dynamic approaches. In relation with the objectives of the present report, static simulations performed routinely upon the resolution of the time‐independent Schrödinger's equation, are based on a solute either embedded in a solvent continuum, or surrounded by a number of explicit water molecules .…”