The long-term goal of this project is to understand the assembly of two membrane proteins with oligomeric structures which differ fundamentally from most studied previously. Both model receptors, the human asialoglycoprotein receptor (ASGP-R) major subunit H1 and the human type II transforming growth factor-Beta receptor (TGF-Beta IIR), have the unusual characteristic of forming homo- and heterooligomers, which they require for function. The ASGP-R is a mammalian liver receptor which binds and internalizes damaged circulating glycoproteins in preparation for degradation. Its major subunit H1 trimerizes in the endoplasmic reticulum and is expressed on the cell surface, but requires the addition of a minor subunit, H2, in order to bind the complex oligosaccharide groups of its typical ligands. The subunit geometry within the receptor complex is highly ordered, although the sequences which mediate homo- and heterooligomerization are unknown. TGF-Beta IIR is a broadly distributed protein which binds TGF-Beta, thereby influencing cell growth differentiation and possibly inhibiting tumorigenesis. It forms homooligomers and heterooligomers (with the type I and type III TGF-Beta receptors), although the timing, subcellular location, and sequences involved are unknown. This project aims to: (1) define the regions and specific residues of the ASGP-R which participate in oligomer formation; and (2) define the composition of TGF-Beta IIR oligomers, determine where they form, and identify which sequences interact during oligomerization. The oligomer- forming ability of chimeric proteins will enable the identification of regions important in oligomer formation; individual residues will be examined by site-directed mutagenesis. Oligomers will be detected by cross-linking mutated proteins made in transfected cells and in vitro, by sucrose-density gradient centrifugation, and by immunofluorescence and co-patching studies on live transfected cells. Understanding the process of oligomer formation will provide insights into the structure of these two important receptors and will ultimately lead to an understanding of the relationship between their structure and function.
| Wells, R G (2000) Fibrogenesis. V. TGF-beta signaling pathways. Am J Physiol Gastrointest Liver Physiol 279:G845-50 |
| Wells, R G; Gilboa, L; Sun, Y et al. (1999) Transforming growth factor-beta induces formation of a dithiothreitol-resistant type I/Type II receptor complex in live cells. J Biol Chem 274:5716-22 |
| Gilboa, L; Wells, R G; Lodish, H F et al. (1998) Oligomeric structure of type I and type II transforming growth factor beta receptors: homodimers form in the ER and persist at the plasma membrane. J Cell Biol 140:767-77 |
| Wells, R G; Yankelev, H; Lin, H Y et al. (1997) Biosynthesis of the type I and type II TGF-beta receptors. Implications for complex formation. J Biol Chem 272:11444-51 |
