Cloning of a human cDNA encoding a novel enzyme involved in the elongation of long-chain polyunsaturated fatty acids

Abstract

The Saccharomyces cerevisiae protein ELO2p is involved in the elongation of saturated and monounsaturated fatty acids. Among several sequences with limited identity with the S. cerevisiaeELO2 gene, a consensus cDNA sequence was identified from the LifeSeq® database of Incyte Pharmaceuticals, Inc. Human liver cDNA was amplified by PCR using oligonucleotides complementary to the 5´ and 3´ ends of the putative human cDNA sequence. The resulting full-length sequence, termed HELO1, consisted of 897bp, which encoded 299 amino acids. However, in contrast with the ELO2 gene, expression of this open reading frame in S. cerevisiae demonstrated that the encoded protein was involved in the elongation of long-chain polyunsaturated fatty acids, as determined by the conversion of γ-linolenic acid (C18:3, n-6) into dihomo-γ-linolenic acid (C20:3, n-6), arachidonic acid (C20:4, n-6) into adrenic acid (C22:4, n-6), stearidonic acid (C18:4, n-3) into eicosatetraenoic acid (C20:4, n-3), eicosapentaenoic acid (C20:5, n-3) into ω3-docosapentaenoic acid (C22:5, n-3) and α-linolenic acid (C18:3, n-3) into ω3-eicosatrienoic acid (C20:3, n-3). The predicted amino acid sequence of the open reading frame had only 29% identity with the yeast ELO2 sequence, contained a single histidine-rich domain and had six transmembrane-spanning regions, as suggested by hydropathy analysis. The tissue expression profile revealed that the HELO1 gene is highly expressed in the adrenal gland and testis. Furthermore, the HELO1 gene is located on chromosome 6, best known for encoding the major histocompatibility complex, which is essential to the human immune response.