海水鱼真鲷脂蛋白脂肪酶基因cDNA序列与组织表达

The cDNA Sequence and Tissue Expression of Lipoprotein Lipase Gene of a Marine Fish, Red Sea Bream (Pagrus major)

为研究脊椎动物真鲷脂蛋白脂肪酶 (LPL)结构与功能关系以及探讨动脉粥样硬化形成机理 ,通过构建cDNA文库 ,克隆对动脉粥样硬化表现抗性的海水鱼真鲷LPL基因cDNA全序列 .再通过PCR方法扩增基因组DNA ,获取内含子 9及其两侧序列以确定外显子 10的大小 ,最后通过RT PCR ,以 β肌动蛋白为外参照 ,比较真鲷在食用两种脂肪含量不同饲料和摄食状态不同的处理条件下 ,肝脏和腹腔肠系膜脂肪组织LPLmRNA的相对水平 .从腹腔肠系膜脂肪组织cDNA文库中克隆出LPLcDNA序列 ,其完整的开放阅读框架由 15 36bp组成 ,编码 5 11个氨基酸残基 .与哺乳类不同 ,真鲷LPL基因外显子 10的开始部分是翻译的 .LPL的催化位点、二硫键位点、N 糖基化位点、肝素结合区、脂质结合位点、介导脂蛋白与低密度脂蛋白受体结合位点、二聚体形成位点等主要功能域在真骨鱼类真鲷与其它脊椎动物间基本保守 ,但肝素结合区的碱性氨基酸残基含量较人类减少 ,并在结合脂质底物的疏水环套中出现插入片段 .与哺乳类不同 ,真鲷LPL基因在成体肝脏存在诱导性表达 ,而在其腹腔肠系膜脂肪组织则存在与哺乳类相似的组成性表达 .当真鲷喂食高脂饲料时 ,其饱食状态下肝脏LPLmRNA水平升高 ,但对其腹腔肠系膜脂肪组织LPL表达没有影响 .当真鲷喂食标准商业饲料时 ,?

To investigate the structural and functional relationship of vertebrate lipoprotein lipase (LPL) and the mechanism for the development of atherosclerosis, LPL cDNA was cloned from a visceral mesenteric adipose cDNA library of a marine fish, red sea bream ( Pagrus major) , which shows resistant to atherosclerosis. Genomic DNA of intron 9 was cloned by PCR to determine the boundary of exon 9 and exon 10. The nutritional regulation of the LPL gene expression was studied in the liver and the visceral mesenteric adipose tissues by RT PCR, using β actin as an external control. The complete open reading frame contains 1 536 bp and encodes for the lipoprotein lipase (511 amino acid residues)cloned from the cDNA library. Unlike mammals, the exon 10 of the fish LPL gene is partially translated. The main domains (catalytic site, disulfide bridge, N glycosylation site, heparin binding domain, lipid binding site, role in bridging lipoproteins to their receptors and site of dimer formation) are basically conserved between the teleost fish and other vertebrates. But basic amino acids are less frequent in the heparin binding domain of the fish LPL than that of the human LPL. Furthermore, there is an insertion of 7 amino acids in the hydrophobic loop of the fish LPL. Unlike mammals, the adult liver of red sea bream showed substantially inductive LPL gene expression whereas the visceral mesenteric adipose tissues showed a similar constitutional LPL gene expression to mammals. High fat diets stimulated LPL gene expression in the liver under fed condition but had no effect in the visceral mesenteric adipose tissues of the fish. Starvation (at 48 hours post feeding) drastically stimulated LPL gene expression in the liver of the fish fed standard commercial diet but decreased it in its visceral mesenteric adipose tissues. The results demonstrate the adaptive LPL expression in the fish liver and structural difference in the heparin binding domain and lipid binding site between the fish LPL and human LPL, which might be related to the insusceptibility of fish (that prefer to utilize large amounts of fat) to atherosclerosis.