Molecular cloning and expression of cDNA encoding rat brain cytosolic acyl-coenzyme A thioester hydrolase.

The cDNA encoding rat brain cytosolic acyl-CoA thioester hydrolase (ACT) has been cloned and sequenced, and the primary structure of the enzyme has been deduced. A partial amino acid sequence (38 amino acids) of the enzyme was determined using the peptides generated after CNBr digestion of the purified enzyme. Primers synthesized on the basis of this information were used to isolate two cDNA clones, each encoding the full length of the enzyme. The nucleotide sequences of these clones contained an open reading frame encoding a 358-amino acid polypeptide with a calculated molecular mass of 39.7 kDa, similar to that determined for the purified enzyme (40.9 kDa). The deduced ACT sequence showed no homology to the known sequences of any other thioesterases nor to any other known protein sequence. However, there was a strong homology to a number of expressed sequence tag human brain cDNA clones. The identity of the ACT cDNA was confirmed by the expression of ACT activity in Escherichia coli. There was a 10-15-fold increase in ACT-specific activity in the bacterial extracts after induction with isopropyl thiogalactoside, and the properties of the expressed enzyme (fusion protein) were the same as those of the purified rat brain ACT. Northern blot analysis showed that a 1.65-kilobase ACT transcript was present in rat brain and testis but not in any other rat tissues examined. However, the ACT mRNA was induced in the liver of rats that were fed Wy-14,643, a peroxisome proliferator and inducer of rodent liver cytosolic acyl-CoA thioesterase. These results indicate that the induced rat liver ACT is homologous to the constitutive rat brain ACT.