Very long-chain acyl-CoA synthetases - Human "bubblegum" represents a new family of proteins capable of activating very long-chain fatty acids

Activation by thioesterification to coenzyme A is a prerequisite for most r eactions involving fatty acids. Enzymes catalyzing activation, acyl-CoA syn thetases, have been classified by their chain length specificities, The mos t recently identified family is the very long-chain acyl-CoA synthetases (V LCS), Although several members of this group are capable of activating very long-chain fatty acids (VLCFA), one is a bile acid-CoA synthetase,and othe rs have been characterized as fatty acid transport proteins, It was reporte d that the Drosophila melanogaster mutant bubblegum (BGM) had elevated VLCF A and that the product of the defective gene had sequence homology to acyl- CoA synthetases. Therefore, we cloned full-length cDNA for a human homolog of BGM, and we investigated the properties of its protein product, hsBG, to determine whether it had VLCS activity. Northern blot analysis showed that hsBG is expressed primarily in brain, Compared with vector-transfected cel ls, COS-l cells expressing hsBG; had increased acyl-CoA synthetase activity with either long-chain fatty acid (2.4-fold) or VLCFA (2.6-fold) substrate s, Despite this increased VLCFA activation, hsBG-expressing cells did not h ave increased rates of VLCFA degradation, Confocal microscopy showed that h sBG had a cytoplasmic localization in some COS-1 cells expressing the prote in, whereas it appeared to associate with plasma:membrane in others, Fracti onation of these cells revealed that most of the hsBG-dependent acyl-CoA sy nthetase activity was soluble and not membrane-bound. Immunoaffinity-purifi ed hsBG from transfected COS-1 cells was enzymatically active, hsBG and hsV LCS are only 15% identical, and comparison with sequences of two: conserved motifs from all known families of acyl-CoA synthetases revealed that hsBG along with the D, melanogaster and murine homologs comprise a new family of acyl-CoA synthetases, Thus, two protein families: are now known that conta in enzymes capable of activating VLCFA. Because hsBG is expressed in brain but previously described VLCSs were not highly expressed in this organ, hsB G may play a central role in brain VLCFA metabolism and myelinogenesis.