title: Reorganization of cellular retinol-binding protein type 1 and lecithin:retinol acyltransferase during retinyl ester biosynthesis.
abstract: BACKGROUND
  Cellular retinol-binding protein, type 1 (Crbp1), chaperones retinyl ester (RE) biosynthesis catalyzed by lecithin:retinol acyltransferase (LRAT).
  
  
  METHODS
  We monitored the subcellular loci of LRAT and Crbp1 before and during RE biosynthesis, and compared the results to diacylglycerol:acyltransferase type 2 (DGAT2) during triacylglycerol biosynthesis in three cell lines: COS7, CHO and HepG2.
  
  
  RESULTS
  Before initiation of RE biosynthesis, LRAT distributed throughout the endoplasmic reticulum (ER), similar to DGAT2, and Crpb1 localized with mitochondria associated membranes (MAM), surrounded by LRAT. Upon initiating RE biosynthesis in cells transfected with low amounts of vector to simulate physiological expression levels, Crpb1 remained with MAM, and both Crbp1 and MAM re-localized with LRAT. LRAT formed rings around the growing lipid droplets. LRAT activity was higher in these rings relative to the general ER. LRAT-containing rings colocalized with the lipid-droplet surface proteins, desnutrin/adipose triglyceride lipase and perilipin 2. Colocalization with lipid droplets required the 38 N-terminal amino acid residues of LRAT, and specifically K36 and R38. Formation of rings around the growing lipid droplets did not require functional microtubules.
  
  
  CONCLUSIONS
  These data indicate a relationship between LRAT and Crbp1 during RE biosynthesis in which MAM-associated Crpb1 and LRAT colocalize, and both surround the growing RE-containing lipid droplet. The N-terminus of LRAT, especially K36 and R38, is essential to colocalization with the lipid droplet.
authors.affiliation: Graduate Program in Metabolic Biology, Nutritional Sciences and Toxicology, College of Natural Resources, University of California, Berkeley, CA 94720-3104, USA.
authors.forename: Weiya
authors.initials: W
authors.lastname: Jiang
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Napoli
mesh_terms: D000217:Acyltransferases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004952:Esters / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D056945:Hep G2 Cells; D006801:Humans; D008870:Microtubules / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000378:metabolism*; D010957:Plasmids; D054840:Retinol-Binding Proteins, Cellular / Q000235:genetics / Q000378:metabolism*; D014801:Vitamin A / Q000031:analogs & derivatives / Q000378:metabolism*
chemical_list: D004952:Esters; D054840:Retinol-Binding Proteins, Cellular; D014801:Vitamin A; D000217:Acyltransferases; C056942:lecithin-retinol acyltransferase