Hydrophobic Mismatch Drives the Interaction of E5 with the Transmembrane Segment of PDGF Receptor.
The oncogenic E5 protein from bovine papillomavirus is a short (44 amino acids long) integral membrane protein that forms homodimers. It activates platelet-derived growth factor receptor (PDGFR) β in a ligand-independent manner by transmembrane helix-helix interactions. The nature of this recognition event remains elusive, as numerous mutations are tolerated in the E5 transmembrane segment, with the exception of one hydrogen-bonding residue. Here, we examined the conformation, stability, and alignment of the E5 protein in fluid lipid membranes of substantially varying bilayer thickness, in both the absence and presence of the PDGFR transmembrane segment. Quantitative synchrotron radiation circular dichroism analysis revealed a very long transmembrane helix for E5 of ∼26 amino acids. Oriented circular dichroism and solid-state (15)N-NMR showed that the alignment and stability of this unusually long segment depend critically on the membrane thickness. When reconstituted alone in exceptionally thick DNPC lipid bilayers, the E5 helix was found to be inserted almost upright. In moderately thick bilayers (DErPC and DEiPC), it started to tilt and became slightly deformed, and finally it became aggregated in conventional DOPC, POPC, and DMPC membranes due to hydrophobic mismatch. On the other hand, when E5 was co-reconstituted with the transmembrane segment of PDGFR, it was able to tolerate even the most pronounced mismatch and was stabilized by binding to the receptor, which has the same hydrophobic length. As E5 is known to activate PDGFR within the thin membranes of the Golgi compartment, we suggest that the intrinsic hydrophobic mismatch of these two interaction partners drives them together. They seem to recognize each other by forming a closely packed bundle of mutually aligned transmembrane helices, which is further stabilized by a specific pair of hydrogen-bonding residues.
Institute of Biological Interfaces (IBG-2), Karlsruhe Institute of Technology, Karlsruhe, Germany.
Dirk
D
Windisch
Institute of Organic Chemistry, Karlsruhe Institute of Technology, Karlsruhe, Germany.
Colin
C
Ziegler
Institute of Biological Interfaces (IBG-2), Karlsruhe Institute of Technology, Karlsruhe, Germany.
Stephan L
SL
Grage
Institute of Biological Interfaces (IBG-2), Karlsruhe Institute of Technology, Karlsruhe, Germany.
Jochen
J
Bürck
Institute of Organic Chemistry, Karlsruhe Institute of Technology, Karlsruhe, Germany.
Marcel
M
Zeitler
National High Magnetic Field Laboratory, Tallahassee, Florida.
Peter L
PL
Gor'kov
Institute of Biological Interfaces (IBG-2), Karlsruhe Institute of Technology, Karlsruhe, Germany; Institute of Organic Chemistry, Karlsruhe Institute of Technology, Karlsruhe, Germany. Electronic address: anne.ulrich@kit.edu.
Anne S
AS
Ulrich
D002942:Circular Dichroism; D004926:Escherichia coli; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D008051:Lipid Bilayers / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D011487:Protein Conformation; D055550:Protein Stability; D017479:Receptors, Platelet-Derived Growth Factor / Q000737:chemistry*
D008051:Lipid Bilayers; D017479:Receptors, Platelet-Derived Growth Factor