Human acyl-CoA dehydrogenase-9 plays a novel role in the mitochondrial β-oxidation of unsaturated fatty acids
Human acyl-CoA dehydrogenase-9 plays a novel role in the mitochondrial β-oxidation of unsaturated fatty acids
复制标题
DOI：
10.1074/jbc.m504460200
复制
发表时间：
2005-09-16
影响因子：
4.8
通讯作者：
Vockley, J
中科院分区：
文献类型：
--
作者：
Ensenauer, R;He, M;Vockley, J
不饱和脂肪酸在预防糖尿病、肥胖、癌症和神经退行性疾病等人类疾病方面发挥着重要作用。然而，它们在体内被酰基辅酶A脱氢酶（ACADs）氧化，所述酰基辅酶A脱氢酶（ACADs）催化线粒体脂肪酸β-氧化的每个循环的第一步还不完全清楚。最近，一个新的ACAD（ACAD-9）的未知功能，是高度同源的人极长链酰基辅酶A脱氢酶的大规模随机测序鉴定。为了表征其酶的作用，我们在大肠杆菌中表达ACAD-9，纯化它，并确定其底物利用模式。通过前体蛋白的体外线粒体输入研究鉴定了酶的成熟形式的N末端。一个37个氨基酸的前导肽被两个线粒体肽酶连续切割，以产生成熟亚基的预测分子量为65 kDa。亚线粒体分馏研究发现，天然ACAD-9与线粒体膜相关。凝胶过滤分析表明，与极长链酰基辅酶A脱氢酶一样，ACAD-9是二聚体，而其他已知的ACADs是四聚体。纯化的成熟ACAD-9以长链不饱和酰基辅酶A（C16：1-、C18：1-、C18：2-、C22：6-CoA）为底物具有最大活性。这些结果表明ACAD-9在长链不饱和脂肪酸的线粒体β-氧化中的先前未被认识的作用。由于ACAD-9在大脑中的底物特异性和丰度，我们推测它可能在脂膜不饱和脂肪酸的周转中发挥作用，而脂膜不饱和脂肪酸对膜完整性和结构至关重要。
Unsaturated fatty acids play an important role in the prevention of human diseases such as diabetes, obesity, cancer, and neurodegeneration. However, their oxidation in vivo by acyl-CoA dehydrogenases (ACADs) that catalyze the first step of each cycle of mitochondrial fatty acid beta-oxidation is not entirely understood. Recently, a novel ACAD (ACAD-9) of unknown function that is highly homologous to human very-long-chain acyl-CoA dehydrogenase was identified by large-scale random sequencing. To characterize its enzymatic role, we have expressed ACAD-9 in Escherichia coli, purified it, and determined its pattern of substrate utilization. The N terminus of the mature form of the enzyme was identified by in vitro mitochondrial import studies of precursor protein. A 37-amino acid leader peptide was cleaved sequentially by two mitochondrial peptidases to yield a predicted molecular mass of 65 kDa for the mature subunit. Submitochondrial fractionation studies found native ACAD-9 to be associated with the mitochondrial membrane. Gel filtration analysis indicated that, like very-long-chain acyl-CoA dehydrogenase, ACAD-9 is a dimer, in contrast to the other known ACADs, which are tetramers. Purified mature ACAD-9 had maximal activity with long-chain unsaturated acyl-CoAs as substrates (C16:1-, C18:1-, C18:2-, C22:6-CoA). These results suggest a previously unrecognized role for ACAD-9 in the mitochondrial beta-oxidation of long-chain unsaturated fatty acids. Because of the substrate specificity and abundance of ACAD-9 in brain, we speculate that it may play a role in the turnover of lipid membrane unsaturated fatty acids that are essential for membrane integrity and structure.