Biochemical Defects in 11-cis-Retinol Dehydrogenase Mutants Associated with Fundus Albipunctatus

Abstract

Mutations in the gene encoding 11-cis-retinol dehydrogenase (RDH5; EC 1.1.1.105) are associated with fundus albipunctatus, an autosomal recessive eye disease characterized by stationary night blindness and accumulation of white spots in the retina. In addition, some mutated alleles are associated with development of cone dystrophy, especially in elderly patients. The numbers of identified RDH5 mutations linked to fundus albipunctatus have increased considerably during recent years. In this work, we have characterized the biochemical and cell biological properties of 11 mutants of RDH5 to understand the molecular pathology of the disease. All RDH5 mutants showed decreased protein stability and subcellular mislocalization and, in most cases, loss of enzymatic activity in vitro and in vivo. Surprisingly, mutant A294P displays significant enzymatic activity. Cross-linking studies and molecular modeling showed that RDH5 is dimeric, and co-expression analyses of wild-type and mutated alleles showed that the mutated enzymes, in a transdominant-negative manner, influenced the in vivo enzymatic properties of functional variants of the enzyme, particularly the A294P mutant. Thus, under certain conditions, nonfunctional alleles act in a dominantnegative way on functional but relatively unstable mutated alleles. However, in heterozygous individuals carrying one wild-type allele, the disease is recessive, probably due to the stability of the wild-type enzyme.

Understanding Retinol Metabolism: Structure and Function of Retinol Dehydrogenases

“…Studies on the related SDR member CRAD1 have confirmed, by independent techniques, that this enzyme has a lumenal topology of the catalytic domain (28,29). Moreover, genetic and biochemical data, as well as computer-based modeling, suggest that these enzymes occur as functional homodimers (29,30).…”

Rpe65 Isomerase Associates with Membranes through an Electrostatic Interaction with Acidic Phospholipid Headgroups

“…These enzymes are located in the ER of RPE cells. Lecithin:retinol acyltransferase and 11-cis-RDH are integral membrane proteins (27,28). The mechanism whereby Rpe65 associates with membranes is the subject of this study.…”

A Novel Homozygous Gly107Arg Mutation in the RDH5 Gene in a Japanese Patient with Fundus albipunctatus with Sectorial Retinitis pigmentosa

“…Identification of a mutation in the RDH5 gene in patients with fundus albipunctatus suggests that reduction in the activity of this enzyme is responsible for the delayed dark adaptation that is seen in this disorder [6]. In vitro experiments showed reduced activity in the enzyme protein produced by mutant 11-cis-retinol dehydrogenase, though knockout mice did not develop yellow-white dot retinal lesions [6,13,14]. It remains to be determined why such characteristic yellow-white dot lesions develop in fundus albipunctatus.…”