Grove, T.J.*; Sidell, B.D.: Signature Motif and Fatty Acid Selectivity of Fatty Acyl CoA Synthetase in Antarctic Fishes

Cardiac and oxidative skeletal muscles of Antarctic notothenioid fishes preferentially utilize lipids over carbohydrates as their main fuel for aerobic metabolism. These tissues further show a marked tendency to oxidize mono-unsaturated fatty acids over saturated fatty acids. We hypothesize that fatty acyl CoA synthetase (FACS; EC 6.2.1.3) may be the primary site dictating specificity for oxidation of long chain unsaturated fatty acids in notothenioids. Full-length FACS cDNAs from oxidative skeletal muscle of Chaenocephalus aceratus, Gobionotothen gibberifrons, and Notothenia coriiceps were identified by RACE PCR and sequenced. Predicted proteins are 697-699 amino acids in length, with 66-67% and 66-69% identity to rat and human, respectively. Part of the fatty acid binding pocket is encoded by a 25-amino acid consensus sequence or “signature motif,” ¹DGWLHTGDIGXWXPXGXLKIIDRKK²⁵, which is common to all FACS. This region from three notothenioids, ⁵³²DGWLHTGDV/IGKWLPNGCLKITDRKK⁵⁵⁶, has 76% (N. coriiceps) to 80% (G. gibberifrons and C. aceratus) identity to the consensus sequence. In all three species examined, the non-polar Ile²¹ of the consensus sequence is changed to a polar Thr⁵⁵¹ residue. This amino acid difference may significantly impact preference for long chain unsaturated fatty acids. Additional amino acid substitutions in this binding motif may also play a role in determining the enzyme’s specificity for both chain length and degree of saturation. These roles will be examined by site-directed mutagenesis. Functional studies of the enzymes to determine substrate specificities are currently underway. Supported by NSF grant OPP 94-21657 and OPP 99-09055 to BDS.