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Christian Salesse, Akio Yamazaki, Eric Demers; Preferential membrane binding of phosphodiesterase 6 compared to other photoreceptor proteins. Invest. Ophthalmol. Vis. Sci. 2018;59(9):2355.
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© ARVO (1962-2015); The Authors (2016-present)
Phosphodiesterase 6 (PDE6) hydrolyzes cGMP during phototransduction cascade, which ultimately leads to photoreceptor hyperpolarization. PDE6 is acylated with a farnesyl as well as a geranylgeranyl group. It is thus a membrane-bound peripheral protein. It was found to be located, at least in part, in detergent-resistant membrane microdomains, which likely contain a large amount of phospholipids with saturated fatty acyl chains. This work was thus aiming to characterize the membrane binding properties of PDE6 and to compare its behavior with that of other photoreceptor proteins associated with disk membranes.
PDE6 was injected into the subphase underneath different phospholipid monolayers with various fatty acyl chains and polar head groups such as those present in the outer segments of photoreceptors. PDE6 binding was monitored by surface pressure measurements to determine its maximum insertion pressure (MIP). Infrared measurements were performed to provide information on the secondary structure and orientation of PDE6.
Measurements of MIP were performed with PDE6 bearing either two (inactive form) or only one (active form) regulatory γ subunit. Much larger values of MIP were obtained for the active than the inactive form of PDE6 in the presence of phospholipids with saturated fatty acyl chains. Both forms of PDE6 showed a small affinity for the polyunsaturated phospholipids of photoreceptors. The values of MIP of the inactive form of PDE6 are smaller than the lateral pressure of membranes. In contrast, values larger than the lateral pressure of membranes have been obtained with the active form of PDE, thus suggesting that the active form of PDE6 binds more strongly the membrane than its inactive form. The infrared spectra are showing a large content of alpha helical secondary structure and an orientation of PDE where most of its alpha helices are parallel with the plane of the membrane. A model of this orientation using the available pdb structure of PDE6 based on its reconstituted individual elements will be presented. This behavior will be compared to that of other photoreceptor proteins.
The large affinity of PDE6 for phospholipids bearing saturated fatty acyl chains, in particular for its active form, suggest that it could be associated with microdomains. This behavior is very similar to that observed for RP2 but very different from that of recoverin and RDH8.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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