Recent studies have provided evidence that peptides as short as tripeptides do adopt preferred conformations. Here we report that the tripeptide Ala-Phe-Ala (AFA) in aqueous solution preferentially forms an inverse Á-turn. Circular dichroism (CD) indicated the presence of a predominant turn structure, and Fourier transform infrared (FTIR) bands suggested the presence of a g-turn forming a bifurcated H-bond with the solvent molecules. The high-resolution structure was obtained by a combined use of NMR spectroscopy and calculations. On the basis of 30 unambiguous ROESY-derived distance restraints (including the Ha-NH NOE between Ala1 and Ala3 and a hydrogen bond between the CO group of Ala1 and the NH group of Ala3), calculations clearly demonstrated the presence of an inverse g-turn centered on Phe2. From NOE data, we estimated a mole fraction for the g-turn of 0.65. Since for AFA an extended b-strand was also reported [Eker, F., Griebenow, K., Cao, X., Nafie, L. A., and Schweitzer-Stenner, R. (2004) Proc. Natl. Acad. Sci. U.S.A. 101, 10054-10059], we investigated the possibility that g-turn and-strand may represent two major conformations. By using a best-fit procedure that calculated experimental NOEs as weighted averages of the effects originating from both structures, we were able to calculate with good accuracy the backbone NOEs at 280 K in terms of the two limiting conformers, yielding a mole fraction for the Á-turn and -strand conformations of 0.60 and 0.40, respectively, in good agreement with those found by NOE data. The implication of the existence of a preferred conformation by a small structural element is discussed in the context of the nucleation of protein folding events and the design of small peptide and peptidomimetic drugs.
The preferred conformation of the tripeptide Ala-Phe-Ala in water is an inverse g-turn: implications for protein folding and drug design
MOTTA A;Andreotti G;
2005
Abstract
Recent studies have provided evidence that peptides as short as tripeptides do adopt preferred conformations. Here we report that the tripeptide Ala-Phe-Ala (AFA) in aqueous solution preferentially forms an inverse Á-turn. Circular dichroism (CD) indicated the presence of a predominant turn structure, and Fourier transform infrared (FTIR) bands suggested the presence of a g-turn forming a bifurcated H-bond with the solvent molecules. The high-resolution structure was obtained by a combined use of NMR spectroscopy and calculations. On the basis of 30 unambiguous ROESY-derived distance restraints (including the Ha-NH NOE between Ala1 and Ala3 and a hydrogen bond between the CO group of Ala1 and the NH group of Ala3), calculations clearly demonstrated the presence of an inverse g-turn centered on Phe2. From NOE data, we estimated a mole fraction for the g-turn of 0.65. Since for AFA an extended b-strand was also reported [Eker, F., Griebenow, K., Cao, X., Nafie, L. A., and Schweitzer-Stenner, R. (2004) Proc. Natl. Acad. Sci. U.S.A. 101, 10054-10059], we investigated the possibility that g-turn and-strand may represent two major conformations. By using a best-fit procedure that calculated experimental NOEs as weighted averages of the effects originating from both structures, we were able to calculate with good accuracy the backbone NOEs at 280 K in terms of the two limiting conformers, yielding a mole fraction for the Á-turn and -strand conformations of 0.60 and 0.40, respectively, in good agreement with those found by NOE data. The implication of the existence of a preferred conformation by a small structural element is discussed in the context of the nucleation of protein folding events and the design of small peptide and peptidomimetic drugs.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
