Mammalian type opsin 5 preferentially activates G14 in Gq-type G proteins triggering intracellular calcium response

Mammalian type opsin 5 (Opn5m), a UV-sensitive G protein-coupled receptor opsin highly conserved in vertebrates, would provide a common basis for UV sensing from lamprey to humans. However, G protein coupled with Opn5m remains controversial due to variations in assay conditions and the origin of Opn5m across different reports. Here, we examined Opn5m from diverse species using an aequorin luminescence assay and G alpha-KO cell line. Beyond the commonly studied major G alpha classes, G alpha q, G alpha 11, G alpha 14, and G alpha 15 in the Gq class were individually investigated in this study, as they can drive distinct signaling pathways in addition to a canonical calcium response. UV light triggered a calcium response via all the tested Opn5m proteins in 293T cells, which was abolished by Gq-type G alpha deletion and rescued by cotransfection with mouse and medaka Gq-type G alpha proteins. Opn5m preferentially activated G alpha 14 and close relatives. Mutational analysis implicated specific regions, including alpha 3-beta 5 and alpha G-alpha 4 loops, alpha G and alpha 4 helices, and the extreme C terminus, in the preferential activation of G alpha 14 by Opn5m. FISH revealed co-expression of genes encoding Opn5m and G alpha 14 in the scleral cartilage of medaka and chicken eyes, supporting their physiological coupling. This suggests that the preferential activation of G alpha 14 by Opn5m is relevant for UV sensing in specific cell types.