Ca super(2+)-Dependent Metarhodopsin Inactivation Mediated by Calmodulin and NINAC Myosin III

• Published in: Neuron (Cambridge, Mass.) Mass.), 2008-09, Vol.59 (5), p.778-789
• Main Authors: Liu, Che-Hsiung, Satoh, Akiko K, Postma, Marten, Huang, Jiehong, Ready, Donald F, Hardie, Roger C
• Format: Article
• Language: English
• Subjects: Drosophila
• ISSN: 0896-6273
• DOI: 10.1016/j.neuron.2008.07.007

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 super(*)) in whole-cell recordings from Drosophila photoreceptors by measuring the time window within which inactivating M super(*) by photoreisomerization to rhodopsin could suppress responses to prior illumination. M super(*) was inactivated rapidly ( tau [inline image]20 ms) under control conditions, but [inline image]10-fold more slowly in Ca super(2+)-free solutions. This pronounced Ca super(2+) dependence of M super(*) inactivation was unaffected by mutations affecting phosphorylation of rhodopsin or arrestin but was abolished in mutants of calmodulin (CaM) or the CaM-binding myosin, NINAC. This suggests a mechanism whereby Ca super(2+) influx acting via CaM and NINAC accelerates the binding of arrestin to M super(*). Our results indicate that this strategy promotes quantum efficiency, temporal resolution, and fidelity of visual signaling.