Ca2+-dependent metarhodopsin inactivation mediated by calmodulin and NINAC myosin III |
| |
Authors: | Liu Che-Hsiung Satoh Akiko K Postma Marten Huang Jiehong Ready Donald F Hardie Roger C |
| |
Affiliation: | Department of Physiology, Development and Neuroscience, Cambridge University, Cambridge CB23DY, UK. |
| |
Abstract: | Phototransduction in flies is the fastest known G protein-coupled signaling cascade, but how this performance is achieved remains unclear. Here, we investigate the mechanism and role of rhodopsin inactivation. We determined the lifetime of activated rhodopsin (metarhodopsin = M( *)) in whole-cell recordings from Drosophila photoreceptors by measuring the time window within which inactivating M( *) by photoreisomerization to rhodopsin could suppress responses to prior illumination. M( *) was inactivated rapidly (tau approximately 20 ms) under control conditions, but approximately 10-fold more slowly in Ca2+-free solutions. This pronounced Ca2+ dependence of M( *) inactivation was unaffected by mutations affecting phosphorylation of rhodopsin or arrestin but was abolished in mutants of calmodulin (CaM) or the CaM-binding myosin III, NINAC. This suggests a mechanism whereby Ca2+ influx acting via CaM and NINAC accelerates the binding of arrestin to M( *). Our results indicate that this strategy promotes quantum efficiency, temporal resolution, and fidelity of visual signaling. |
| |
Keywords: | |
本文献已被 PubMed 等数据库收录! |
|