Disease relevance of LRAT

• PURPOSE: To determine the structure of the human lecithin retinol acyltransferase (LRAT) gene, map its chromosomal localization, and screen for mutations in humans with various hereditary retinal degenerations [1].

High impact information on LRAT

• The studies reveal new roles for palmitoylated proteins as molecular switches and LRAT as a palmitoyl transferase whose role is to catalyze the mRPE65 to sRPE65 conversion [2].
• Tissue distribution analysis by Northern blot showed expression of a 5.0-kilobase transcript in the human retinal pigment epithelium as well as in other tissues that are known for their high LRAT activity and vitamin A processing [3].
• High performance liquid chromatography analysis of the reaction product formed by HEK-293 cells transfected with LRAT cDNA confirmed the ability of the transfected cells to convert [3H]all-trans-retinol into authentic [3H]all-trans-retinyl palmitate as chemically determined [3].
• The enzyme responsible for conversion of all-trans-retinol into retinyl esters, the lecithin retinol acyltransferase (LRAT) has been characterized at the molecular level [3].
• Although the microsomal preparation exhibited LRAT activity, acyl transfer was not readily reversible as labeled palmitic acid was not transferred to added acyl acceptor compounds [4].

Biological context of LRAT

• The human LRAT gene was localized to chromosome 4q31.2, a locus having no previous association with human eye disease [1].
• RESULTS: The human LRAT gene is organized into three exons of 219, 541, and 2058 bp and two introns of 103 and 4117 bp [1].
• Fluorescence in situ hybridization (FISH) analysis of normal metaphase chromosomes derived from phytohemagglutinin (PHA) stimulated peripheral blood lymphocytes and radiation hybrid mapping were used for localization of the LRAT gene [1].
• METHODS: Using DNA probes specific for LRAT, a bacterial artificial chromosome (BAC) clone containing the LRAT gene was isolated, subcloned into DNA fragments and relevant subclones characterized by sequencing [1].
• Lecithin retinol acyltransferase (LRAT) catalyzes the esterification of all-trans-retinol into all-trans-retinyl ester, an essential reaction in the vertebrate visual cycle [5].

Anatomical context of LRAT

• The almost quantitative extraction of RPE65 from RPE membranes has little or no effect on in vitro LRAT and isomerohydrolase activities in quantitative enzymatic assays using RPE membranes, suggesting that RPE65 may not have an important role to play in the enzymatic processing of all-trans-retinol into 11-cis-retinol in vitro [6].
• Lecithin retinol acyl transferase (LRAT) from the retinyl pigment epithelium is potently inhibited by all-trans-retinyl alpha-bromoacetate in the micromolar range [7].
• The purpose of this study is to investigate if a readily available cell line (APRE-19) may be used to study in vitro function of visual cycle enzymes such as lecithin:retinol acyltransferase (LRAT) [8].

Associations of LRAT with chemical compounds

• When retinyl esters were allowed to form prior to the addition of the LRAT inhibitors, a significant amount of isomerization product was generated [9].
• The two critical RPE enzymes in the isomerization pathway are lecithin retinol acyl transferase (LRAT) and isomerohydrolase, which processes all-trans-retinyl esters into 11-cis-retinol [6].
• Treatment of crude bovine RPE membranes with (3R)-3-[boc-lys(biotinyl)-O]-all-trans-retinol chloroacetate 1 in the low micromolar range led to the specific labeling of RPE65 and lecithin retinol acyltransferase (LRAT) [10].
• LRAT proved to be broadly specific for retinols but was relatively inert with other hydrophobic alcohols including cholesterol [11].
• Site-specific mutagenic experiments on the lysine and tyrosine residues of LRAT reveal that only the highly conserved tyrosine 154 is essential for catalytic activity [12].

Analytical, diagnostic and therapeutic context of LRAT

• Southern blot analysis of digested genomic DNA revealed a single band, suggesting a single copy of the LRAT gene [1].
• Gene microarray and Western blot results indicated that ARPE-19 cells expressed LRAT transcript and the LRAT protein [8].

References