HUMAN ACETYL-COA CARBOXYLASE-2 - MOLECULAR-CLONING, CHARACTERIZATION,CHROMOSOMAL MAPPING, AND EVIDENCE FOR 2 ISOFORMS

cDNA encoding the 280-kDa acetyl-CoA carboxylase 2 (ACC2) isoform was isolated from human Liver using the polymerase chain reaction. Sequenc ing the cDNA revealed an open reading frame of 7,449 base pairs (bp) t hat encode 2,483 amino acids (M-r 279,380). Using 5-kilobase pair cDNA clones as probes, we localized the gene encoding the 280-kDa human ca rboxylase to chromosome 12q23. When the cDNA of ACC was compared with that of ACC1, the nucleotide sequences and the predicted amino acid se quences had about 60 and 80% identity, respectively. Ser(77) and Ser(7 9), which were found to be critical for the phosphorylation and subseq uent inactivation of rat ACC1 (Ser(78) and Ser(80) of human ACC1), are conserved in ACC2 and are represented as Ser(219) and Ser(221), respe ctively. On the other hand, Ser(1200), which is also a phosphorylation site in rat ACC1 (Ser(1201) of human ACC1), is not conserved in ACC2. The homology between the amino acid sequences of the two human carbox ylases, however, is primarily found downstream of residues Ser(78) and Ser(81) in human ACC1 and their equivalents, that is Ser(219) and Ser (221) in ACC2, suggesting that the sequence of the first 218 amino aci ds at the N terminus of ACCB represents a unique peptide that accounts , in part, for the variance between the two carboxylases. Using a cDNA probe (400 bp) that encodes the N-terminal amino acid residues of ACC 2 in Northern blot analyses of different human and mouse tissues showe d that ACC2 is predominantly expressed in liver, heart, and the skelet al muscles. Polyclonal antibodies raised against the N-terminal peptid e (amino acid residues 1-220) reacted specifically and equally with hu man and rat ACC2 carboxylases, confirming the uniqueness of this N-ter minal peptide and its conservation in animal ACC2. In addition, we pre sent evidence for the presence of an isoform of ACC2 (M-r 270,000) in human liver that differs from the 280-kDa ACC2 by the absence of 303 n ucleotides that encode 101 amino acids in the region between Arg(1114) and Asp(1215). The regulation and physiological significance of the t wo ACC2 isoforms remain to be determined.