Structure-based minimization of transforming growth factor-alpha (TGF-alpha) through NMR analysis of the receptor-bound ligand. Design, solution structure, and activity of TGF-alpha 8-50.
The investigation of a N-terminally truncated human transforming growth factor-alpha (TGF-alpha; residues 8-50) has been completed to determine the contribution of the N terminus to receptor binding and activation. The deletion protein was proposed and designed through study of NMR relaxation and nuclear Overhauser enhancement data obtained from the TGF-alpha-epidermal growth factor (EGF) receptor complex, which indicated that the residues N-terminal to the A loop remain flexible in receptor-bound TGF-alpha and thus suggested their lack of involvement in receptor binding (Hoyt, D. W., Harkins, R. N., Debanne, M. T., O'Connor-McCourt, M., and Sykes, B. D. (1994) Biochemistry 33, 15283-15292; McInnes, C., Hoyt, D. W., Harkins, R. N., Pagila, R. N., Debanne, M. T., O'Connor-McCourt, M., and Sykes, B. D. (1996) J. Biol. Chem. 271, 32204-32211). TGF-alpha 8-50 was shown to have approximately 10-fold lower affinity for the receptor than the native molecule in an assay quantifying the ability to compete with EGF for binding and to have a similar reduction in activity as indicated by a cell proliferation assay. NMR solution structural calculations on this molecule demonstrate correct formation of the three disulfide bonds of TGF-alpha 8-50 and have established the presence of native secondary structure in the B and C loops of the protein. However, some perturbation of the global fold with respect to the orientation of the subdomains was observed. These results suggest that although the N-terminal residues do not contribute directly to binding, they make a significant contribution in defining the conformation of the growth factor, which is required for complete binding and activity and is therefore significant in terms of producing native folding of TGF-alpha. They also show that information obtained from the receptor-bound ligand can be used to guide the design and minimization of TGF-alpha analogues. The implications of the study of TGF-alpha 8-50 for the design and synthesis of reductants of this growth factor are therefore discussed.
McInnes
C
C
Protein Engineering Network of Centres of Excellence, 713 Heritage Medical Research Centre, University of Alberta, Edmonton, Alberta T6G 2S2, Canada.
Wang
J
J
Al Moustafa
A E
AE
Yansouni
C
C
O'Connor-McCourt
M
M
Sykes
B D
BD
D000595:Amino Acid Sequence; D001667:Binding, Competitive; D002460:Cell Line; D003198:Computer Simulation; D066246:ErbB Receptors / Q000737:chemistry*; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000737:chemistry* / Q000494:pharmacology; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011522:Protons; D012996:Solutions; D013499:Surface Properties; D016211:Transforming Growth Factor alpha / Q000737:chemistry* / Q000494:pharmacology
D008024:Ligands; D010446:Peptide Fragments; D011522:Protons; D012996:Solutions; D016211:Transforming Growth Factor alpha; C115149:transforming growth factor-alpha (8-50); D066246:ErbB Receptors