Human Cellular Retinaldehyde-Binding Protein Has Secondary Thermal 9-Cis-Retinal Isomerase Activity.
Bolze, C.S., Helbling, R.E., Owen, R.L., Pearson, A.R., Pompidor, G., Dworkowski, F., Fuchs, M.R., Furrer, J., Golczak, M., Palczewski, K., Cascella, M., Stocker, A.(2014) J Am Chem Soc 136: 137
- PubMed: 24328211
- DOI: https://doi.org/10.1021/ja411366w
- Primary Citation of Related Structures:
4CIZ, 4CJ6 - PubMed 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.
Organizational Affiliation:
Department of Chemistry and Biochemistry, and ‡Graduate School for Cellular and Biomedical Sciences, University of Bern , Freiestrasse 3, 3012 Bern, Switzerland.