Penrose J F, Baldasaro M H, Webster M, Xu K, Austen K F, Lam B K
Division of Rheumatology, Immunology, and Allergy, Brigham and Women's Hospital, Boston, MA, USA.
Eur J Biochem. 1997 Sep 15;248(3):807-13. doi: 10.1111/j.1432-1033.1997.00807.x.
Leukotriene C4 (LTC4) synthase (LTC4S), an integral membrane protein, catalyzes the conjugation of leukotriene A4 with reduced glutathione to form LTC4, the biosynthetic parent of the additional cysteinyl leukotriene metabolites. An XmnI-digested fragment of a P1 clone from a 129 mouse ES library contained the full-length gene of 2.01 kb for mouse LTC4S. The mouse LTC4S gene is comprised of 5 exons of 122, 100, 71, 82 and 241 nucleotides, with intron sizes that range from 76 nucleotides to 937 nucleotides. The intron/exon boundaries are identical to those of the human genes for LTC4S and 5-lipoxygenase-activating protein (FLAP). Primer extension demonstrated a single transcription-initiation site 64 bp 5' of the ATG translation-start site. Nucleotide sequencing of 1.2 kb of the 5' flanking region revealed multiple putative sites for activating protein-2, CCAAT/enhancer-binding protein, and polyoma virus enhancer-3. Fluorescent in situ hybridization mapped the mouse LTC4S gene to mouse chromosome 11, in a region containing the genes for interleukin 13 and granulocyte/macrophage-colony-stimulating factor, and orthologous to the chromosomal location of 5q35 for the human LTC4S gene. Thus, the mouse LTC4S gene is similar in size, intron/exon organization and chromosomal localization to the human LTC4S gene. Recent mutagenic analysis of the conjugation function of human LTC4S has identified R51 and Y93 as critical for acid and base catalysis of LTA4 and reduced glutathione, respectively. A comparison across species for proteins that possess LTC4S activity reveals conservation of both of these residues, whereas R51 is absent in the FLAP molecules. Thus, within the glutathione S-transferase superfamily of genes, alignment of specific residues allows the separation of LTC4S family members from their most structurally similar counterparts, the FLAP molecules.
白三烯C4（LTC4）合酶（LTC4S）是一种整合膜蛋白，催化白三烯A4与还原型谷胱甘肽结合形成LTC4，LTC4是其他半胱氨酰白三烯代谢产物的生物合成前体。来自129小鼠胚胎干细胞文库的一个P1克隆经XmnI酶切后的片段包含小鼠LTC4S的全长2.01 kb基因。小鼠LTC4S基因由122、100、71、82和241个核苷酸的5个外显子组成，内含子大小从76个核苷酸到937个核苷酸不等。内含子/外显子边界与人类LTC4S和5-脂氧合酶激活蛋白（FLAP）基因的边界相同。引物延伸显示在ATG翻译起始位点上游64 bp处有一个单一的转录起始位点。对5'侧翼区域1.2 kb的核苷酸测序揭示了多个激活蛋白-2、CCAAT/增强子结合蛋白和多瘤病毒增强子-3的假定位点。荧光原位杂交将小鼠LTC4S基因定位到小鼠11号染色体上，该区域包含白细胞介素13和粒细胞/巨噬细胞集落刺激因子的基因，并且与人类LTC4S基因在染色体5q35的定位同源。因此，小鼠LTC4S基因在大小、内含子/外显子组织和染色体定位上与人类LTC4S基因相似。最近对人类LTC4S结合功能的诱变分析已确定R51和Y93分别对LTA4和还原型谷胱甘肽的酸碱催化至关重要。对具有LTC4S活性的蛋白质进行的跨物种比较揭示了这两个残基的保守性，而FLAP分子中不存在R51。因此，在谷胱甘肽S-转移酶基因超家族中，特定残基的比对允许将LTC4S家族成员与其结构上最相似的对应物FLAP分子区分开来。
