Conformation of thymosin beta 4 in water determined by NMR spectroscopy

The conformational preferences of a 43-amino-acid G-actin-binding peptide, thymosin beta 4, in water at 1, 4 and 14 degrees C, and at pH 3.0 and 6.5 were studied by NMR. NMR showed that thymosin beta 4 lacks a uniquely folded conformation in water. However, some preferential alpha-helical conformations of thymosin beta 4 can be observed in aqueous solutions. The segment at residues 5-16 showed characteristic interactions for conformations in both the beta-strand and alpha-helical regions of the phi-psi space, based on strong C alpha H(i)-NH(i+1) interactions and NH-NH, C alpha H(i)-NH(i+3), and C alpha H(i)-C beta H(i+3) interactions, respectively. At 1-4 degrees C, another segment at residues 31-37 also shows both beta and alpha conformations, forming however a less well-defined helix than the segment at residues 5-16. At 14 degrees C, the conformational population of the helix at positions 5-16 is shifted more towards the random and turn-like structures, whereas the segment at positions 31-37 becomes exclusively a random coil.