title: Activity of the acyl-CoA synthetase ACSL6 isoforms: role of the fatty acid Gate-domains.
abstract: BACKGROUND
  Activation of fatty acids by acyl-CoA synthetase enzymes is required for de novo lipid synthesis, fatty acid catabolism, and remodeling of biological membranes. Human long-chain acyl-CoA synthetase member 6, ASCL6, is a form present in the plasma membrane of cells. Splicing events affecting the amino-terminus and alternative motifs near the ATP-binding site generate different isoforms of ACSL6.
  
  
  RESULTS
  Isoforms with different fatty acid Gate-domain motifs have different activity and the form lacking this domain, isoform 3, showed no detectable activity. Enzymes truncated of the first 40 residues generate acyl-CoAs at a faster rate than the full-length protein. The gating residue, which prevents entry of the fatty acid substrate unless one molecule of ATP has already accessed the catalytic site, was identified as a tyrosine for isoform 1 and a phenylalanine for isoform 2 at position 319. All isoforms, with or without a fatty acid Gate-domain, as well as recombinant protein truncated of the N-terminus, can interact to form enzymatic complexes with identical or different isoforms.
  
  
  CONCLUSIONS
  The alternative fatty acid Gate-domain motifs are essential determinants for the activity of the human ACSL6 isoforms, which appear to act as homodimeric enzyme as well as in complex with other spliced forms. These findings provide evidence that the diversity of these enzyme species could produce the variety of acyl-CoA synthetase activities that are necessary to generate and repair the hundreds of lipid species present in membranes.
authors.affiliation: Children's Hospital Oakland Research Institute, Oakland, California 94609, USA. esoupene@chori.org
authors.forename: Eric
authors.initials: E
authors.lastname: Soupene
authors.forename: Nghi Phuong
authors.initials: NP
authors.lastname: Dinh
authors.forename: Melvin
authors.initials: M
authors.lastname: Siliakus
authors.forename: Frans A
authors.initials: FA
authors.lastname: Kuypers
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D003066:Coenzyme A Ligases / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism; D017830:Octoxynol / Q000378:metabolism; D010649:Phenylalanine / Q000378:metabolism; D017434:Protein Structure, Tertiary; D014443:Tyrosine / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D014443:Tyrosine; D010649:Phenylalanine; D000255:Adenosine Triphosphate; D017830:Octoxynol; D003066:Coenzyme A Ligases; C403665:ACSL6 protein, human