Sequence-specific ¹H-NMR assignments and identification of two small antiparallel β-sheets in the solution structure of recombinant human transforming growth factor α

Transforming growth factor α (TGFα) is a small mitogenic protein with about 35% sequence identity with epidermal growth factor (EGF). TGFα-like proteins have been proposed to play a role in oncogenesis and wound healing. This report describes sequence-specific ¹H-NMR resonance assignments for recombinant human TGFα (hTGFα). These assignments provide the basis for interpreting NMR data which demonstrate that the solution structure of hTGFα includes an antiparallel β-sheet involving residues Gly-19 to Leu-24 and Lys-29 to Cys-34 and a second, smaller, antiparallel β-sheet involving residues Tyr-38 and Val-39 and His-45 and Ala-46. These data, together with constraints imposed by the disulfide bonds, are combined to construct a molecular model of the polypeptide chain fold for residues Cys-8 to Ala-46. The resulting structure is similar to that of mouse and human EGF. Human TGFα and mouse EGF, however, differ with respect to their structural dynamics, since amide proton/deuteron exchange is much faster for hTGFα than for mouse EGF at pH 3.5.