MUTAGENESIS ANALYSIS OF THE MEMBRANE-PROXIMAL LIGAND-BINDING SITE OF THE TGF-BETA RECEPTOR-TYPE-III EXTRACELLULAR DOMAIN

There are two TGF-beta binding subdomains in the extracellular domain of receptor type LII (proximal acid distal in relation to the transmem brane domain). Here vie present an extension of our analysis of the pr oximal binding site of receptor type III, Due to the original deletion mutagenesis strategy, our proximal binding site contained 19 amino ac ids from the N-terminal part of the receptor, By deleting these, we de monstrated that they did not contribute to the binding ability of the proximal binding site. We also produced a soluble, secreted form of th e proximal binding site and demonstrated that it was able to bind TGF- beta, Finally, we analyzed the role of the three asparagine residues ( 580, 591, 595) that are located in the region of the receptor that is necessary for expression of a functional proximal binding site, and fo und that mutation of these residues individually to alanine did not af fect ligand binding.