High impact information on BAAT

• Inheritance seems to be oligogenic, with genotype at BAAT modifying penetrance in individuals homozygous with respect to the mutation in TJP2 [1].
• We used immunofluorescence microscopy and digitonin permeabilization assays to determine the subcellular location of endogenous BAAT in primary human and rat hepatocytes [2].
• Bile acid-coenzyme A:amino acid N-acyltransferase (BAAT) is the sole enzyme responsible for conjugation of primary and secondary bile acids to taurine and glycine [2].
• Previous studies indicate a peroxisomal location of BAAT in peroxisomes with variable amounts up to 95% detected in cytosolic fractions [2].
• When expressed in fibroblasts, GFP-tagged hBAAT localized to the cytosol, confirming earlier observations [2].

Biological context of BAAT

• A specific immunoaffinity-purified rabbit anti-hBAT polyclonal antibody was used to screen a lambda Zap XR human liver cDNA library resulting in the isolation of two unique clones. hBAT8 and hBAT9 (1669 and 1491 base pairs in length, respectively) were isolated following screening of 4 x 10(5) clones of the cDNA library [3].

Anatomical context of BAAT

• Green fluorescent protein localization experiments in human skin fibroblasts showed that the hBACAT enzyme is mainly cytosolic [4].
• Conclusion: hBAAT and rBaat are peroxisomal enzymes present in undetectable amounts in the cytosol [2].
• The existence of a very active long-chain fatty acyl-CoA hydrolase in homogenates of human blood platelets is reported [5].

Associations of BAAT with chemical compounds

• We therefore hypothesized that hBACAT may also hydrolyze fatty acyl-CoAs and/or conjugate fatty acids to glycine [4].
• Treatment with NEM caused inactivation of wild-type hBAT [6].
• Although substitution of Cys-235 with serine generated an hBAT mutant with lower N-acyltransferase activity, it substantially increased the bile acid-CoA thioesterase activity compared with wild type [6].
• Substitution of His-362 or Asp-328 with alanine results in inactivation of hBAT [6].
• However, preincubation of wild-type hBAT with the substrate cholyl-CoA before NEM treatment prevented loss of N-acyltransferase activity [6].

Other interactions of BAAT

• In summary, data from this study support the existence of an essential catalytic triad within hBAT consisting of Cys-235, His-362, and Asp-328 with Cys-235 serving as the probable nucleophile and thus the site of covalent attachment of the bile acid molecule [6].
• kan-1 (bile acid CoA:amino acid N-acyltransferase) messenger RNA as a novel predictive indicator for prognosis of hepatocellular carcinoma patients after partial hepatectomy [7].

Analytical, diagnostic and therapeutic context of BAAT

• Using a rabbit polyclonal antibody raised against the purified enzyme, Western blot analysis using 100,000 x g human liver supernatant confirmed that the affinity-purified polyclonal antibody was specific for human liver bile acid-CoA:amino acid N-acyltransferase [8].
• Glycine and taurine conjugation of bile acids by a single enzyme. Molecular cloning and expression of human liver bile acid CoA:amino acid N-acyltransferase [3].
• In the present study, the function of the putative catalytic triad of hBAT was examined by chemical modification with the cysteine alkylating reagent N-ethylmaleimide (NEM) and by site-directed mutagenesis of the triad residues followed by enzymology studies of mutant and wild-type hBATs [6].
• Sequence analysis showed no similarity to known esterases, but a high degree (approx. 40%) of identity with bile acid-CoA:amino acid N-acyltransferase cloned from human and rat liver [9].

References