Signal transduction in the visual cascade involves specific lipid-protein interactions.
In retinal rod photoreceptor cells, transducin (Gt) and cyclic GMP phosphodiesterase (PDE) are peripherally anchored to the cytoplasmic surface of the disk saccules. We have examined the role of specific phospholipids in the interaction of these proteins with native osmotically intact disk vesicles, employing spin-labeled phospholipid analogues (2% of total phospholipids) and bovine serum albumin back-exchange assay. Inactive GDP-bound transducin exclusively reduced the extraction of negatively charged phosphatidylserine. The effect disappeared upon activation of the G-protein with guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS). PDE affected the extraction of the zwitterionic phosphatidylcholine and, to a smaller extent, of phosphatidylethanolamine. When active GtGTPgammaS interacted with the PDE to form the active effector, the interaction with phosphatidylcholine was specifically enhanced. Each copy of the G-protein bound 3 +/- 1 molecules of phosphatidylserine, whereas the PDE bound a much larger amount (70 +/- 10) of a mixture of phosphatidylcholine and ethanolamine. The results are interpreted as a head group-specific and state-dependent interaction of the signaling proteins with the phospholipids of the photoreceptor membrane.
Hessel
Elke
E
Institut für Medizinische Physik und Biophysik, Universitätsklinikum Charité, Humboldt Universität zu Berlin, Ziegelstrasse 5-9, 10098 Berlin, Germany. elke.hessel@charite.de
Heck
Martin
M
Müller
Peter
P
Herrmann
Andreas
A
Hofmann
Klaus Peter
KP
D000818:Animals; D002417:Cattle; D003624:Darkness; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D007700:Kinetics; D008051:Lipid Bilayers; D015227:Lipid Peroxidation; D008958:Models, Molecular; D010743:Phospholipids / Q000378:metabolism*; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D011487:Protein Conformation; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology*; D012710:Serum Albumin, Bovine / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D013113:Spin Labels; D015293:Transducin / Q000737:chemistry / Q000378:metabolism*; D014785:Vision, Ocular / Q000502:physiology*
D008051:Lipid Bilayers; D010743:Phospholipids; D013113:Spin Labels; D012710:Serum Albumin, Bovine; D010727:Phosphoric Diester Hydrolases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D015293:Transducin