Compensatory mutants of the bovine papillomavirus E5 protein and the platelet-derived growth factor β receptor reveal a complex direct transmembrane interaction.
The 44-amino-acid E5 protein of bovine papillomavirus is a dimeric transmembrane protein that exists in a stable complex with the platelet-derived growth factor (PDGF) β receptor, causing receptor activation and cell transformation. The transmembrane domain of the PDGF β receptor is required for complex formation, but it is not known if the two proteins contact one another directly. Here, we studied a PDGF β receptor mutant containing a leucine-to-isoleucine substitution in its transmembrane domain, which prevents complex formation with the wild-type E5 protein in mouse BaF3 cells and inhibits receptor activation by the E5 protein. We selected E5 mutants containing either a small deletion or multiple substitution mutations that restored binding to the mutant PDGF β receptor, resulting in receptor activation and growth factor independence. These E5 mutants displayed lower activity with PDGF β receptor mutants containing other transmembrane substitutions in the vicinity of the original mutation, and one of them cooperated with a receptor mutant containing a distal mutation in the juxtamembrane domain. These results provide strong genetic evidence that the transmembrane domains of the E5 protein and the PDGF β receptor contact one another directly. They also demonstrate that different mutations in the E5 protein allow it to tolerate the same mutation in the PDGF β receptor transmembrane domain and that a mutation in the E5 protein can allow it to tolerate different mutations in the PDGF β receptor. Thus, the rules governing direct interactions between transmembrane helices are complex and not restricted to local interactions.
Department of Genetics, Yale School of Medicine, New Haven, Connecticut, USA.
Anne P B
AP
Edwards
Yanhua
Y
Xie
Lara
L
Bowers
Daniel
D
DiMaio
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D002417:Cattle; D002460:Cell Line; D004252:DNA Mutational Analysis; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000378:metabolism*; D025941:Protein Interaction Mapping; D017479:Receptors, Platelet-Derived Growth Factor / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion
D050505:Mutant Proteins; D009856:Oncogene Proteins, Viral; C054304:oncogene protein E5, Bovine papillomavirus type 1; D017479:Receptors, Platelet-Derived Growth Factor