Bolze CS Helbling RE Owen RL Pearson AR Pompidor G Dworkowski F Fuchs MR Furrer J Golczak M Palczewski K Cascella M Stocker A 2014 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. application/pdf https://sonar.ch/global/documents/86551 eng info:eu-repo/semantics/altIdentifier/doi/10.1021/ja411366w info:eu-repo/semantics/altIdentifier/pmid/24328211 info:eu-repo/semantics/openAccess Journal of the American Chemical Society. - 2014 Carrier Proteins Chromatography, High Pressure Liquid Crystallography, X-Ray Diterpenes Humans Isomerases Kinetics Magnetic Resonance Spectroscopy Models, Molecular Quantum Theory Retinaldehyde Substrate Specificity Human cellular retinaldehyde-binding protein has secondary thermal 9-cis-retinal isomerase activity. http://purl.org/coar/resource_type/c_6501