The conformation of peptide thymosin alpha 1 in solution and in a membrane-like environment by circular dichroism and NMR spectroscopy. A possible model for its interaction with the lymphocyte membrane.

The 28-residue peptide thymosin alpha1 was studied by circular dichroism and two-dimensional NMR. Circular dichroism indicates that thymosin alpha1 in water solution does not assume a preferred conformation, while in the presence of small unilamellar vesicles of dimiristoylphosphatidylcholine and dimiristoylphosphatidic acid (10:1) and in sodium dodecyl sulphate, it assumes a partly structured conformation. Presence of zinc ions produces similar effects. In a more hydrophobic environment like a solution of a mixed solvent water-2,2,2 trifluoroethanol, it adopts a structured conformation. NMR spectra indicated that in this mixture as solvent, thymosin alpha1 has a structure characterized by two regions. A beta-turn is present between residue 5 and residue 8, while the region between residues 17 and 24 shows an alpha helix conformation. These changes of conformation in different environments may be considered structural requirements in the steps of its interaction with the lymphocyte membrane. In fact, these conformational changes may correspond to the first event of the mechanism of lymphocyte activation in the immune response modulation by thymosin alpha1.