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Real-time Analyses of Retinol Transport by the Membrane Receptor of Plasma Retinol Binding Protein
Published on: January 28, 2013
Structures important in NAD(P)(H) specificity for mammalian retinol and 11-Cis-retinol dehydrogenases
1Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla 92093, USA.
Abstract:
Mammalian retinol and 11-cis retinol dehydrogenases catalyze the formation of retinaldehyde from retinol and 11-cis retinaldehyde from 11-cis retinol, respectively. Although their amino acid sequences are 54% identical, these enzymes have different cofactor specificities: rat retinol dehydrogenase uses NADP+, while cow 11-cis retinol dehydrogenase uses NAD+. We used their close sequence similarity and the availability of 3D structures of their homologs to construct a 3D model of the two retinol dehydrogenases to investigate the determinants for cofactor specificity. The structure of rat retinol dehydrogenase shows that lysine-64 is important in stabilizing binding of 2'-phosphate on NADP+ in two ways: lysine's positively charged side chain has a coulombic attraction to the 2'-phosphate and partially compensates for the negative charge of aspartic acid-38. Cow 11-cis retinol dehydrogenase has threonine-61 at the position homologous to lysine-64. Threonine-61 does not have a stabilizing coulombic interaction with NADP+, nor can threonine-61 counteract the repulsive interaction between NADP+ and aspartic acid-37 in 11-cis retinol dehydrogenase. This suggests that aspartic acid-37 and threonine-61 are important in the specificity of 11-cis retinol dehydrogenase for NAD+.
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