O K, Hill J S, Wang X, Pritchard P H
Department of Pathology, University of British Columbia, Vancouver, Canada.
J Lipid Res. 1993 Jan;34(1):81-8.
Fish-eye disease is a rare genetic disorder of high density lipoprotein (HDL) metabolism that is characterized biochemically by a partial deficiency of the enzyme lecithin:cholesterol acyltransferase (LCAT). One of the mutations that is causative for fish-eye disease occurs at codon 123 of the LCAT gene. This mutation results in the exchange of a threonine residue for an isoleucine in the LCAT protein (Thr123-->Ile). In order to understand the functional significance of this exchange, we have used site-directed mutagenesis to reconstruct this mutation in an LCAT cDNA followed by expression of the mutant LCAT in COS-1 cells. The fish-eye disease mutation resulted in a 50% decrease in LCAT mass in the culture medium compared to wild type enzyme. The secreted mutant protein was incapable of esterifying cholesterol in HDL and HDL analogues. However, this protein retained the ability to esterify cholesterol in plasma and low density lipoprotein. These results support the hypothesis that this mutation is responsible for biochemical abnormalities of LCAT observed in fish-eye disease and the mutant LCAT protein has lost the potential to esterify cholesterol in the HDL pool but retains the ability to esterify cholesterol from other lipoproteins.
鱼眼病是一种罕见的高密度脂蛋白（HDL）代谢遗传性疾病，其生化特征是卵磷脂胆固醇酰基转移酶（LCAT）部分缺乏。导致鱼眼病的其中一种突变发生在LCAT基因的第123密码子处。这种突变导致LCAT蛋白中的苏氨酸残基被异亮氨酸取代（Thr123→Ile）。为了了解这种取代的功能意义，我们利用定点诱变技术在LCAT cDNA中重建这种突变，随后在COS-1细胞中表达突变型LCAT。与野生型酶相比，鱼眼病突变导致培养基中LCAT质量减少50%。分泌的突变蛋白无法使HDL和HDL类似物中的胆固醇酯化。然而，这种蛋白保留了使血浆和低密度脂蛋白中的胆固醇酯化的能力。这些结果支持了这样的假说，即这种突变是鱼眼病中观察到的LCAT生化异常的原因，并且突变型LCAT蛋白已经失去了使HDL池中的胆固醇酯化的潜力，但保留了使其他脂蛋白中的胆固醇酯化的能力。
