The acuH gene of Aspergillus nidulans , required for growth on acetate and long-chain fatty acids, encodes a putative homologue of the mammalian carnitine/acylcarnitine carrier

Abstract

The Aspergillus nidulans acuH gene, required for growth on acetate and long-chain fatty acids, was cloned by complementation of the acuH13 mutation. Northern blotting analysis showed that transcription of the acuH gene occurs in acetate-grown mycelium and at higher levels in oleate-grown mycelium, but not during growth on glucose minimal medium. The acuH gene encodes a protein of 326 amino acids that belongs to the mitochondrial carrier family. The ACUH protein contains three related segments of approximately 100 amino acids in length, each segment comprising two hydrophobic domains that are probably folded into two transmembrane alpha-helices linked by an extensive polar region. Sequence comparisons suggest that the acuH gene of A. nidulans encodes the homologue of the carnitine/acylcarnitine carrier of rat and man. The uncharacterised proteins YOR100C of Saccharomyces cerevisiae, COLT of Drosophila melanogaster, and DIF-1 of Caenorhabditis elegans also seem to be homologues of ACUH. In addition to the motifs present in all members of the mitochondrial carrier family, we propose the highly conserved motif R(A,S)(V,F)PANAA(T,C)F within the sixth hydrophobic domain of these proteins as the characteristic feature of the carnitine carrier subfamily. The proposed function of the ACUH protein is the transport of acetylcarnitine molecules from the cytosol to the mitochondrial matrix, a process required during growth on acetate or on long-chain fatty acids.

Identification by Site-directed Mutagenesis and Chemical Modification of Three Vicinal Cysteine Residues in Rat Mitochondrial Carnitine/Acylcarnitine Transporter

“…This asymmetric orientation of the membrane-embedded CAC is also supported by functional studies indicating different substrate-binding sites on the inner and outer faces in both intact mitochondria (6) and reconstituted liposomes (7). The CAC is encoded in man by the gene SLC25A20 (2) that maps to chromosome 3p21.31 (8), in Saccharomyces cerevisiae by the gene CRC (9), and in Aspergillus nidulans by the gene acuH (10). The rat CAC gene was expressed in Escherichia coli and refolded in an active form (11), which opened the way to using site-directed mutagenesis to elucidate structure-function relationships of this metabolically important transporter.…”

Regulation of theacuFGene, Encoding Phosphoenolpyruvate Carboxykinase in the Filamentous FungusAspergillus nidulans

“…This is abolished by mutations in the genes facA (acetyl-CoA synthase [2,3]), acuD (isocitrate lyase [3]), facC (cytoplasmic carnitine acetyltransferase [42]), acuJ (peroxosimal and mitochondrial carnitine acetyltransferase [42; M. J. Hynes, unpublished data), and acuH (acetyl carnitine carrier protein [3,15])-all of which result in loss of acetate metabolism via the TCA cycle. In addition, the loss-of-function facB101 mutation affecting acetate induction of genes required for acetate utilization mediated by the facB activator (28,30,43,44) results in the loss of acetate induction.…”

Role of Carnitine Acetyltransferases in Acetyl Coenzyme A Metabolism in Aspergillus nidulans

“…Acetylcarnitine transport into mitochondria is accomplished by Crc1, which is essential for growth on sources of acetyl-CoA in the absence of Cit2 (42,68). Similarly, in A. nidulans the acuH gene, originally identified by acetate/fatty acid nonutilizing mutants, encodes a mitochondrial acetyl-carnitine transporter (3,12,13). No peroxisomal transporters for acetyl-carnitine are known.…”