TGF-β2 uses the concave surface of its extended finger region to bind betaglycan’s ZP domain via three residues specific to TGF-β and inhibin-α

• Published in: The Journal of biological chemistry Vol. 294; no. 9; pp. 3065 - 3080
• Main Authors: Henen, Morkos A., Mahlawat, Pardeep, Zwieb, Christian, Kodali, Ravindra B., Hinck, Cynthia S., Hanna, Ramsey D., Krzysiak, Troy C., Ilangovan, Udayar, Cano, Kristin E., Hinck, Garrett, Vonberg, Machell, McCabe, Megan, Hinck, Andrew P.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.03.2019; American Society for Biochemistry and Molecular Biology
• Subjects: Amino Acid Sequence; Animals; betaglycan; Binding Sites; cardiac development; cell signaling; cell surface receptor; endocrinology; finger region; Humans; Hydrogen-Ion Concentration; ILV methyl labeling; Inhibins - metabolism; Mice; Models, Molecular; nuclear magnetic resonance (NMR); Protein Binding; Protein Domains; Protein Structure, Secondary; Proteoglycans - chemistry; Proteoglycans - metabolism; Rats; Receptors, Transforming Growth Factor beta - chemistry; Receptors, Transforming Growth Factor beta - metabolism; Signal Transduction; Substrate Specificity; Transforming Growth Factor beta2 - chemistry; Transforming Growth Factor beta2 - metabolism; transforming growth factor β (TGF-B); ILV methyl labeling; betaglycan; finger region; nuclear magnetic resonance (NMR); transforming growth factor β (TGF-B); cell signaling; cell surface receptor; cardiac development; endocrinology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.RA118.005210

Betaglycan (BG) is a membrane-bound co-receptor of the TGF-β family that selectively binds transforming growth factor-β (TGF-β) isoforms and inhibin A (InhA) to enable temporal-spatial patterns of signaling essential for their functions in vivo. Here, using NMR titrations of methyl-labeled TGF-β2 with BG’s C-terminal binding domain, BGZP-C, and surface plasmon resonance binding measurements with TGF-β2 variants, we found that the BGZP-C–binding site on TGF-β2 is located on the inner surface of its extended finger region. Included in this binding site are Ile-92, Lys-97, and Glu-99, which are entirely or mostly specific to the TGF-β isoforms and the InhA α-subunit, but they are unconserved in other TGF-β family growth factors (GFs). In accord with the proposed specificity-determining role of these residues, BG bound bone morphogenetic protein 2 (BMP-2) weakly or not at all, and TGF-β2 variants with the corresponding residues from BMP-2 bound BGZP-C more weakly than corresponding alanine variants. The BGZP-C–binding site on InhA previously was reported to be located on the outside of the extended finger region, yet at the same time to include Ser-112 and Lys-119, homologous to TGF-β2 Ile-92 and Lys-97, on the inside of the fingers. Therefore, it is likely that both TGF-β2 and InhA bind BGZP-C through a site on the inside of their extended finger regions. Overall, these results identify the BGZP-C–binding site on TGF-β2 and shed light on the specificity of BG for select TGF-β–type GFs and the mechanisms by which BG influences their signaling.