Disk membranes in the rod photoreceptor cell are loaded with a series of proteins for phototransduction cascade, including rhodopsin (Rh), G-protein transducin (Gt), phosphodiesterase6 (PDE6), rhodopsin kinase (GRK1), and S-modulin (frog of recoverin). Membrane micro-domains, lipid rafts, are believed to regulate the phototransduction by modulating the local accumulation and interactions these proteins. However, the regulation mechanism are poorly understood, partially because the affinities of the proteins to lipid rafts (raftophilicity) are not known.<br/>In this study, we evaluate the raftophilicities of the proteins involved in phototransduction by using a patterned lipid membrane havingliquid ordered (Lo) (raft model) and liquid disordered (Ld) (non-raft model) bilayer domains. We microscopically determined the densities of molecules in the Lo and Ld regions, and quantified the raftophilicities of the proteins, including Rh monomer, Rh dimer, Rh-Gt complex, Gt trimer, Gt a-subunit (Gat), PDE6, and S-modulin. The raftophilicity of Rh increased upon forming a Rh-Gt complex or a dimer, suggesting that Rh accumulate in lipid raft upon photo-activation. On the other hand, raftophilicity of Gat was lower than that of Gt trimer, indicating that Gat dissociates from lipid rafts after photo-activation and migrates toward PDE6, which has a very low raftophilicity. The obtained raftophilicities were generally consistent with the localization of proteins observed in disk membranes. These results should help to evaluate the localization of proteins in the membrane and its influences in modulating the phototransduction rates. We discuss on the implications of varied raftophilicities and the functional roles of lipid rafts.

Evaluating the interactions of lipid raft and proteins involved in phototransduction by using a micropatterned model membrane

253rd National Meeting (2017)

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