CGI-58, The Causative Gene for Chanarin-Dorfman Syndrome, Mediates Acylation of Lysophosphatidic Acid

Comparative Gene Identification–58 (cgi-58) is a member of $\alpha/\beta$-hydrolase family of proteins. Mutations in CGI-58 are shown to be responsible for a rare genetic disorder known as Chanarin-Dorfman syndrome, characterized by an excessive accumulation of triacylglycerol in several tissues and ichthyosis. We have earlier reported that YLR099c encoding Ict1p in Saccharomyces cerevisiae can acylate lysophosphatidic acid to phosphatidic acid. Here we report that human CGI-58 is closely related to ICT1. To understand the biochemical function of cgi-58, the gene was overexpressed in Escherichia coli and the purified recombinant protein was found to specifically acylate lysophosphatidic acid in an acyl-CoA dependent manner. Overexpression of CGI-58 in S. cerevisiae showed an increase in the formation of phosphatidic acid resulting in an overall increase in the total phospholipids. However, triacylglycerol level was found to be significantly reduced. In addition, physiological significance of cgi-58 in mice white adipose tissue was studied. We found soluble lysophosphatidic acid acyltransferase activity in the mice white adipose tissue. Immunoblot analysis using anti-Ict1p antibodies followed by mass spectrometry of the immunocross reactive protein in lipid droplets revealed its identity as cgi-58. These observations suggest the existence of an alternate cytosolic phosphatidic acid biosynthetic pathway in the white adipose tissue. Collectively, these results reveal the role of cgi-58 as an acyltransferase