过氧物酶体多功能酶2中固醇载体蛋白2结构域的功能

过氧物酶体多功能酶 (包括Ⅰ型、Ⅱ型 ,简称MFE1、MFE2 )在哺乳类动物的脂类代谢中发挥其重要作用 .MFE1具有 2 烯酰CoA水合酶 1和 (3S) 羟脂酰CoA脱氢酶的活性 ,而MFE2具有 2 烯酰CoA水合酶 2和 (3R) 羟脂酰CoA脱氢酶的活性 ,两者均催化烯酰CoA在过氧物酶体β 氧化途径中的第 2步和第 3步反应 .MFE1与MFE2的氨基酸序列不具有任何同源性 ,并且它们的底物特异性也不相同 .比较哺乳类MFE1及酵母MFE2发现 ,哺乳类MFE2羧基末端带有由 12 5个残基组成的固醇载体蛋白 2 (简称SCP2 )结构域 ,其功能是未知的 .为了研究SCP2结构域在MFE2中的功能 ,将人MFE2、MFE2ΔSCP2 (删除MFE2中的SCP2 )、脱氢酶结构域、水合酶结构域以及SCP2结构域分别在E .coli中表达 ,并经纯化得到相应的重组蛋白 .通过测定 2 烯酰CoA水合酶 2和 (3R) 羟脂酰CoA脱氢酶对烯酰CoA的催化活性发现 ,带有SCP2结构域的重组蛋白的酶活力及催化效率高于删除SCP2的突变体蛋白 .实验结果表明 ,SCP2结构域可能通过增强MFE2与脂酰CoA的结合力 ,使得MFE2发挥最有效的催化活力

The Function of SCP2-homologous Domain of Human Peroxisomal Multifunctional Enzyme Type 2

Peroxisomal multifunctional enzymes (MFEs) play important roles in lipid metabolism in mammalian peroxisomes. Two MFEs (MFE1 and MFE2) catalyze the second and third reactions of the β-oxidation via the formation of 3-hydroxy intermediates with opposite chirality. Compared with MFE1, MFE2 has an additional SCP2 (sterol carrier protein 2) homologous domain at its C-terminus following the hydratase domain. In order to reveal its physiological function, human MFE2, MFE2ΔSCP2 (deletion of SCP2 in MFE2), dehydrogenase domain, hydratase domain, hydratase domain plus SCP2 homologous domain and SCP2 domain were separately expressed in E.coli and purified. The kinetic data measured with trans-2-decenoyl-CoA and trans-2-hexadecenoyl-CoA show that the SCP2 domain increases the catalytic efficiency of both (3R)-hydroxyacyl-CoA dehydrogenase and 2-enoyl-CoA hydratase 2 activities of MFE2, suggesting that SCP2 domain plays an important role in MFE2 due to its ability of binding long-chain acyl-CoA esters and their derivatives.