title: Human cellular retinaldehyde-binding protein has secondary thermal 9-cis-retinal isomerase activity.
abstract: 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.
authors: Department of Chemistry and Biochemistry, and ‡Graduate School for Cellular and Biomedical Sciences, University of Bern , Freiestrasse 3, 3012 Bern, Switzerland.
authors: Christin S
authors: CS
authors: Bolze
authors: Rachel E
authors: RE
authors: Helbling
authors: Robin L
authors: RL
authors: Owen
authors: Arwen R
authors: AR
authors: Pearson
authors: Guillaume
authors: G
authors: Pompidor
authors: Florian
authors: F
authors: Dworkowski
authors: Martin R
authors: MR
authors: Fuchs
authors: Julien
authors: J
authors: Furrer
authors: Marcin
authors: M
authors: Golczak
authors: Krzysztof
authors: K
authors: Palczewski
authors: Michele
authors: M
authors: Cascella
authors: Achim
authors: A
authors: Stocker
mesh_terms: D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D018360:Crystallography, X-Ray; D004224:Diterpenes; D006801:Humans; D007535:Isomerases / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D011789:Quantum Theory; D012172:Retinaldehyde / Q000737:chemistry*; D013379:Substrate Specificity
chemical_list: C020932:11-cis-retinal-binding protein; D002352:Carrier Proteins; D004224:Diterpenes; C031390:9-cis-retinal; D007535:Isomerases; D012172:Retinaldehyde