TRANSFORMING GROWTH-FACTOR-BETA-1 - 3-DIMENSIONAL STRUCTURE IN SOLUTION AND COMPARISON WITH THE X-RAY STRUCTURE OF TRANSFORMING GROWTH-FACTOR-BETA-2

The three-dimensional solution structure of human transforming growth factor beta 1 (TGF-beta 1) has been determined using multinuclear magn etic resonance spectroscopy and a hybrid distance geometry/simulated a nnealing algorithm. It represents one of the first examples of a mamma lian protein structure that has been solved by isotopic labeling of th e protein in a eukaryotic cell line and multinuclear NMR spectroscopy. The solution structure of the 25 kDa disulfide-linked TGF-beta 1 homo dimer was calculated from over 3200 distance and dihedral angle restra ints. The final ensemble of 33 accepted structures had no NOE or dihed ral angle violations greater than 0.30 Angstrom and 5.0 degrees, respe ctively. The RMSD of backbone atoms for the ensemble of 33 structures relative to their mean structure was 1.1 Angstrom when all residues we re used in the alignment and 0.7 Angstrom when loop regions were omitt ed. The solution structure of TGF-beta 1 follows two independently det ermined crystal structures of TGF-beta 2 (Daopin et al., 1992, 1993; S chlunegger & Grutter, 1992, 1993), providing the first opportunity to examine structural differences between the two isoforms at the molecul ar level. Although the structures are very similar, with an RMSD in ba ckbone atom positions of 1.4 Angstrom when loop regions are omitted in the alignment and 1.9 Angstrom when all residues are considered, ther e are several notable differences in structure and flexibility which m ay be related to function. The dearest example of these is in the p-tu rn from residues 69-72: the turn type found in the solution structure of TGF-beta 1 falls into the category of type II, whereas that present in the X-ray crystal structure of TGF-beta 2 is more consistent with a type I turn conformation. This may be of functional significance as studies using TGF-beta chimeras and deletion mutants indicate that thi s portion of the molecule may be important in receptor binding.