CONFORMATION OF THYMOSIN BETA(4) IN WATER DETERMINED BY NMR-SPECTROSCOPY

The conformational preferences of a 43-amino-acid G-actin-binding pept ide, thymosin beta4, 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 beta4 lacks a un iquely folded conformation in water. However, some preferential alpha- helical conformations of thymosin beta4 can be observed in aqueous sol utions. The segment at residues 5-16 showed characteristic interaction s 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) interaction s and NH-NH, C(alpha)H(i)-NH(i+3), and C(alpha)H(i)-C(beta)H(i+3) inte ractions, 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-degre es-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.