title: Three key residues underlie the differential affinity of the TGFbeta isoforms for the TGFbeta type II receptor.
abstract: TGFbeta1, beta2, and beta3 are 25kDa homodimeric polypeptides that play crucial non-overlapping roles in development, tumor suppression, and wound healing. They exhibit 70-82% sequence identity and transduce their signals by binding and bringing together the TGFbeta type I and type II receptors, TbetaRI and TbetaRII. TGFbeta2 differs from the other isoforms in that it binds TbetaRII weakly and is dependent upon the co-receptor betaglycan for function. To explore the physicochemical basis underlying these differences, we generated a series of single amino acid TbetaRII variants based on the crystal structure of the TbetaRII:TGFbeta3 complex and examined these in terms of their TGFbeta isoform binding affinity and their equilibrium stability. The results showed that TbetaRII Ile53 and Glu119, which contact TGFbeta3 Val92 and Arg25, respectively, together with TbetaRII Asp32, Glu55, and Glu75, which contact TGFbeta3 Arg94, each contribute significantly, between 1 kcal mol(-1) to 1.5 kcal mol(-1), to ligand binding affinities. These contacts likely underlie the estimated 4.1 kcal mol(-1) lower affinity with which TbetaRII binds TGFbeta2 as these three ligand residues are unchanged in TGFbeta1 but are conservatively substituted in TGFbeta2 (Lys25, Ile92, and Lys94). To test this hypothesis, a TGFbeta2 variant was generated in which these three residues were changed to those in TGFbetas 1 and 3. This variant exhibited receptor binding affinities comparable to those of TGFbetas 1 and 3. Together, these results show that these three residues underlie the lowered affinity of TGFbeta2 for TbetaRII and that all isoforms likely induce assembly of the TGFbeta signaling receptors in the same overall manner.
authors.affiliation: Biotechnology Research Institute, National Research Council, Montreal, Que. Canada H4P2R2.
authors.forename: Gregory
authors.initials: G
authors.lastname: De Crescenzo
authors.forename: Cynthia S
authors.initials: CS
authors.lastname: Hinck
authors.forename: Zhanyong
authors.initials: Z
authors.lastname: Shu
authors.forename: Jorge
authors.initials: J
authors.lastname: Zúñiga
authors.forename: Junhua
authors.initials: J
authors.lastname: Yang
authors.forename: Yuping
authors.initials: Y
authors.lastname: Tang
authors.forename: Jason
authors.initials: J
authors.lastname: Baardsnes
authors.forename: Valentín
authors.initials: V
authors.lastname: Mendoza
authors.forename: LuZhe
authors.initials: L
authors.lastname: Sun
authors.forename: Fernando
authors.initials: F
authors.lastname: López-Casillas
authors.forename: Maureen
authors.initials: M
authors.lastname: O'Connor-McCourt
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Hinck
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D009154:Mutation; D011485:Protein Binding; D020033:Protein Isoforms / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*; D055672:Static Electricity; D013816:Thermodynamics; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: D020033:Protein Isoforms; D018125:Receptors, Transforming Growth Factor beta; D016212:Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; D000077294:Receptor, Transforming Growth Factor-beta Type II