XB-ART-54635Biochem J. February 26, 2018;
A novel rhodopsin phosphodiesterase from Salpingoeca rosetta shows light-enhanced substrate affinity.
It is since many years textbook knowledge that the concentration of the second messenger cGMP is regulated in animal rod and cone cells by type-II rhodopsins via a G protein signaling cascade. Microbial rhodopsins with enzymatic activity for regulation of cGMP concentration were only recently discovered: in 2014 light-activated guanylyl cyclase opsins in fungi and in 2017 a novel rhodopsin phosphodiesterase in the protist Salpingoeca rosetta ( Sr RhoPDE). The light-regulation of Sr RhoPDE however, seemed very weak or absent. Here we present strong evidence for light-regulation by studying Sr RhoPDE, expressed in Xenopus laevis oocytes, at different substrate concentrations. Hydrolysis of cGMP shows a ~100-fold higher turnover than that of cAMP. Light causes a strong decrease of the K m value for cGMP from 80 µM to 13 µM but increases the maximum turnover only by ~30%. The PDE activity for cAMP is similarly enhanced by light at low substrate concentrations. Illumination does not affect the cGMP degradation of Lys296 mutants which are not able to form a covalent bond of Schiff base type to the chromophore retinal. We demonstrate that Sr RhoPDE shows cytosolic N- and C-termini, most likely via an eight-transmembrane helix (8-TM) structure. Sr RhoPDE is a new optogenetic tool for light-regulated cGMP manipulation which might be further improved by genetic engineering.
PubMed ID: 29483295
Article link: Biochem J.