Packing contacts can mediate highly specific interactions between artificial transmembrane proteins and the PDGFβ receptor
2007
Ptacek, Jennifer B. | Edwards, Anne P.B. | Freeman-Cook, Lisa L. | DiMaio, Daniel
We used proteins with randomized transmembrane (TM) domains to explore the role of hydrophobic amino acids in mediating specific interactions between transmembrane helices. The 44-aa bovine papillomavirus E5 protein, which binds to the TM domain of the PDGFβ receptor (PDGFβR) was used as a scaffold to construct a library encoding small dimeric proteins with randomized, strictly hydrophobic TM domains, and proteins were selected that induced focus formation in mouse C127 cells by activating the PDGFβR. Analysis of these proteins identified a motif of two hydrophobic residues that, when inserted into a 17-residue polyleucine TM domain, generated a protein that activated the PDGFβR and transformed cells. In addition, we identified transforming proteins that activated the wild-type PDGFβR but did not activate a series of PDGFβR TM point mutants that were efficiently activated by the E5 protein, indicating that these proteins were more specific than the E5 protein. Our results implied that multiple van der Waals interactions distributed along the entire length of the TM domains were required for productive interaction between the PDGFβR and some small proteins lacking hydrophilic TM residues. Our results also suggested that excluding hydrophilic residues from small TM proteins and peptides is a strategy to increase the specificity of heteromeric TM helix-helix interactions.
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