The human bile acid-CoA:amino acid N-acyltransferase functions in the conjugation of fatty acids to glycine.
Bile acid-CoA:amino acid N-acyltransferase (BACAT) catalyzes the conjugation of bile acids to glycine and taurine for excretion into bile. By use of site-directed mutagenesis and sequence comparisons, we have identified Cys-235, Asp-328, and His-362 as constituting a catalytic triad in human BACAT (hBACAT) and identifying BACAT as a member of the type I acyl-CoA thioesterase gene family. We therefore hypothesized that hBACAT may also hydrolyze fatty acyl-CoAs and/or conjugate fatty acids to glycine. We show here that recombinant hBACAT also can hydrolyze long- and very long-chain saturated acyl-CoAs (mainly C16:0-C26:0) and by mass spectrometry verified that hBACAT also conjugates fatty acids to glycine. Tissue expression studies showed strong expression of BACAT in liver, gallbladder, and the proximal and distal intestine. However, BACAT is also expressed in a variety of tissues unrelated to bile acid formation and transport, suggesting important functions also in the regulation of intracellular levels of very long-chain fatty acids. Green fluorescent protein localization experiments in human skin fibroblasts showed that the hBACAT enzyme is mainly cytosolic. Therefore, the cytosolic BACAT enzyme may play important roles in protection against toxicity by accumulation of unconjugated bile acids and non-esterified very long-chain fatty acids.
O'Byrne
James
J
Department of Laboratory Medicine, Division of Clinical Chemistry, Karolinska Institutet, Huddinge University Hospital, SE-141 86 Stockholm, Sweden.
Hunt
Mary C
MC
Rai
Dilip K
DK
Saeki
Masayumi
M
Alexson
Stefan E H
SE
D000217:Acyltransferases / Q000737:chemistry*; D000595:Amino Acid Sequence; D000818:Animals; D001224:Aspartic Acid / Q000737:chemistry; D001647:Bile Acids and Salts / Q000378:metabolism; D002384:Catalysis; D003001:Cloning, Molecular; D003545:Cysteine / Q000737:chemistry; D003600:Cytosol / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D005227:Fatty Acids / Q000737:chemistry; D005347:Fibroblasts / Q000201:enzymology; D005704:Gallbladder / Q000201:enzymology; D005998:Glycine / Q000737:chemistry; D049452:Green Fluorescent Proteins; D006639:Histidine / Q000737:chemistry; D006801:Humans; D007422:Intestines / Q000201:enzymology; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008164:Luminescent Proteins / Q000378:metabolism; D013058:Mass Spectrometry; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013654:Taurine / Q000737:chemistry; D014018:Tissue Distribution
D001647:Bile Acids and Salts; D018076:DNA, Complementary; D005227:Fatty Acids; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D049452:Green Fluorescent Proteins; D013654:Taurine; D001224:Aspartic Acid; D006639:Histidine; D000217:Acyltransferases; C026953:bile acid-CoA amino acid N-acyltransferase; D003545:Cysteine; D005998:Glycine