biostudies-literatureBolze CSNEI NIH HHSSwiss National Science FoundationNational Institutes of HealthBiotechnology and Biological Sciences Research Council137-46https://www.ebi.ac.uk/biostudies/studies/S-EPMC3936205biostudies-literatureUnknown136(1)Cellular retinaldehyde-binding protein (CRALBP) chaperones 11-cis-retinal to convert opsin receptor molecules into photosensitive retinoid pigments of the eye. We report a thermal secondary isomerase activity of CRALBP when bound to 9-cis-retinal. UV/vis and (1)H NMR spectroscopy were used to characterize the product as 9,13-dicis-retinal. The X-ray structure of the CRALBP mutant R234W:9-cis-retinal complex at 1.9 Å resolution revealed a niche in the binding pocket for 9-cis-aldehyde different from that reported for 11-cis-retinal. Combined computational, kinetic, and structural data lead us to propose an isomerization mechanism catalyzed by a network of buried waters. Our findings highlight a specific role of water molecules in both CRALBP-assisted specificity toward 9-cis-retinal and its thermal isomerase activity yielding 9,13-dicis-retinal. Kinetic data from two point mutants of CRALBP support an essential role of Glu202 as the initial proton donor in this isomerization reaction.Journal of the American Chemical SocietyHuman cellular retinaldehyde-binding protein has secondary thermal 9-cis-retinal isomerase activity.PMC3936205BB/H001905/1R01EY020551PP00P2_139195R01EY009339R01 EY02055131003A_130497R01 EY009339Golczak MPearson ARPalczewski KHelbling REDworkowski FCascella MBolze CSOwen RLStocker APompidor GFuchs MRFurrer JfalseHuman cellular retinaldehyde-binding protein has secondary thermal 9-cis-retinal isomerase activity.Cellular retinaldehyde-binding protein (CRALBP) chaperones 11-cis-retinal to convert opsin receptor molecules into photosensitive retinoid pigments of the eye. We report a thermal secondary isomerase activity of CRALBP when bound to 9-cis-retinal. UV/vis and (1)H NMR spectroscopy were used to characterize the product as 9,13-dicis-retinal. The X-ray structure of the CRALBP mutant R234W:9-cis-retinal complex at 1.9 Å resolution revealed a niche in the binding pocket for 9-cis-aldehyde different from that reported for 11-cis-retinal. Combined computational, kinetic, and structural data lead us to propose an isomerization mechanism catalyzed by a network of buried waters. Our findings highlight a specific role of water molecules in both CRALBP-assisted specificity toward 9-cis-retinal and its thermal isomerase activity yielding 9,13-dicis-retinal. Kinetic data from two point mutants of CRALBP support an essential role of Glu202 as the initial proton donor in this isomerization reaction.2014-01-01T00:00:00Z2014 Jan2024-10-18T00:48:08.779Z2019-03-27T01:22:24ZS-EPMC39362052432821110.1021/ja411366w