NMR Structural Studies of Interactions of a Small, Nonpeptidyl Tpo Mimic with the Thrombopoietin Receptor Extracellular Juxtamembrane and Transmembrane Domains

• Published in: The Journal of biological chemistry Vol. 282; no. 19; pp. 14253 - 14261
• Main Authors: Kim, Min-Ju, Park, Sang Ho, Opella, Stanley J., Marsilje, Thomas H., Michellys, Pierre-Yves, Seidel, H. Martin, Tian, Shin-Shay
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 11.05.2007; American Society for Biochemistry and Molecular Biology
• Subjects: Amino Acid Sequence; Carcinoma, Hepatocellular - metabolism; Carcinoma, Hepatocellular - pathology; Cell Membrane; Humans; Liver Neoplasms - metabolism; Liver Neoplasms - pathology; Magnetic Resonance Spectroscopy; Models, Molecular; Molecular Sequence Data; Plasmids; Receptors, Thrombopoietin - chemistry; Receptors, Thrombopoietin - metabolism; Sequence Homology, Amino Acid; Thrombopoietin - chemistry; Thrombopoietin - metabolism; Tumor Cells, Cultured
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M611616200

Thrombopoietin (Tpo) is a glycoprotein growth factor that supports hematopoietic stem cell survival and expansion and is the principal regulator of megakaryocyte growth and differentiation. Several small, nonpeptidyl molecules have been identified as selective human Tpo receptor (hTpoR) agonists. To understand how the small molecule Tpo mimic SB394725 interacts and activates hTpoR, we performed receptor domain swap and mutagenesis studies. The results suggest that SB394725 interacts specifically with the extracellular juxtamembrane region (JMR) and the transmembrane (TM) domain of hTpoR. Solution and solid-state NMR structural studies using a peptide containing the JMR-TM sequences showed that this region of hTpoR, unexpectedly, consists of two α-helices separated by a few nonhelical residues. SB394725 interacts specifically with His-499 in the TM domain and a few distinct residues in the JMR-TM region and affects several specific C-terminal TM domain residues. The unique structural information provided by these studies both sheds light on the distinctive mechanism of action of SB394725 and provides valuable insight into the mechanism of ligand-induced cytokine receptor activation.