CD studies of synthetic polypeptides as histone models: Poly(L-Arg-L-Ile-Gly), poly(L-Arg-L-Nva-Gly), and poly(L-Arg-L-Nle-Gly)
✍ Scribed by Vassilios Tsikaris; Maria Sakarellos-Daitsiotis; Constantinos Sakarellos; Michel Marraud
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1988
- Tongue
- English
- Weight
- 805 KB
- Volume
- 27
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Sequential polypeptides (L-Arg-X-Gly), were prepared as synthetic models of arginine-rich histones t o study their structure and their stereospecific interactions with DNA. In our previous work the conformational characteristics of poly(L-Arg-L-Ala-Gly), poly(L-Arg-L-Val-Gly), and poly( L-Arg-L-Leu-Gly) have already been analyzed. To obtain further insight into the influence of the X residue side chain on the conformation of the (L-Arg-X-Gly), polytripeptides, we now report their synthesis and CD properties when X represents the amino acid residues Ile, Nva, and Nle. The pentachlorophenyl active esters of the appropriate tripeptides were used to perform the polymerization, and the toluene-4-sulfonyl group was used to protect the arginine guanido group. CD spectroscopy showed that, in 100% trifluoroethanol, the degree of helical conformation increased in the order Ile + Nle + Nva. An equilibrium between 8-turn, a-helix, and random-coil conformers occurred in 100% hexafluoroisopropyl alcohol, while a rise in the temperature or the addition of water favored the a-helix, the highest percentage of which was observed in a mixture of hexafluoroisopropyl alcohol :water (20 : 80) and in the order Ile + Nle + Nva. In aqueous solutions (at pH 7 and 12) the polymers behaved as a random coil, but they were forced t o a less aperiodic structure, over a range of ionic strengths (0-0.5M NaF). A rise in temperature of up to 70°C in 100% trifluoroethanol resulted in a decrease of the a-helix percentage of the polymers, while in aqueous solutions the aperiodic structure decreased with increasing temperature. This study proved the importance of the nature of the X residue (length, C, branching) in relation to the structural order of the sequential polypeptides. We concluded that the polymers prepared are suitable models for arginine-rich histones.