24-dehydrocholesterol reductase, the affected enzyme in desmosterolosis, a severe inherited disorder of cholesterol metabolism

Desmosterolosis (OMIM #602398) is a rare recessive disease causing multiple congenital anomalies and mental developmental delays (1). The increased levels of desmosterol, suggest a defect in the enzyme catalyzing the conversion of desmosterol into cholesterol, thus the 24-dehydrocholesterol reductase (DHCR24). The DHCR24 gene (2) was found to be identical with the gene encoding Seladin-1 (from Selective Alzheimer Disease INdicator Protein-1), whose levels are significantly lowered in brain areas damaged in Alzheimer disease (3). Seladin-1 levels also vary in cancer cells and during differentiation, in agreement with its proposed antiapoptotic role. However, the link between the putative DHCR24 enzymatic activity in cholesterol synthesis and the antiapoptotic function is not known yet. On the basis of sequence analyses, Seladin-1/DHCR24 has been proposed to be formed by an N-terminal domain containing two transmembrane helices for its anchoring to the endoplasmic reticulum membrane and a FAD-dependent catalytic domain structurally related to the oxidase/monooxygenases class whose prototype is vanillyl alcohol oxidase. In order to contribute to the elucidation of the biological role of Seladin-1/DHCR24, we initiated a project aimed to produce and characterize its biochemical properties. Therefore, we here present the first attempts to: (i) overproduce soluble and catalytically active forms of Seladin-1/DHCR24 in E. coli and yeast; (ii) carry out subcellular localization studies; (iii) identify protein isoforms and correlate their level and location with the biological functions of Seladin-1/DHCR24. (This work is supported by Telethon grant GGP 10090).