Structure of a Biosynthetic Enzyme for Unsaturated Fatty Acids

用X-射线结晶学方法测定了来自大肠杆菌的酶B-羟基癸酰基硫酯脱水酶的三维结构。这种酶对于在大肠杆菌中通过催化脱水和双键异构化反应生物合成不饱和脂肪酸是必不可少的。该酶因其被3-二十二酸硫醇酯抑制自杀的特性而闻名。这种特定的、不可逆的、共价修饰的酶将被利用来为晶体结构的测定提供重原子标记。通过在缓蚀剂化合物中引入重原子引起的反常色散效应来解决晶体结构问题。目标酶的非常强的衍射晶体表明结构测定可以进行很高的分辨率。因此，将继续进行超低温下的结晶学研究，以便最大限度地确定结构细节。结构测定的结果有望解释该酶对底物酰基的高度专一性，验证单一活性部位负责催化这两个酶反应，指出与其他结合疏水分子的蛋白质可能的相似之处，并提供关于蛋白质分子中原子迁移率的额外数据。

The three-dimensional structure of the enzyme B-hydroxydecanoyl thioester dehydrase from E. coli will be determined by X-ray crystallography. This enzyme is essential for biosynthesis of unsaturated fatty acids in E. coli by catalyzing both dehydration and double-bond isomerization reactions. The enzyme is known for its property of suicide inhibition by thiol esters of 3-decynoic acid. This specific, irreversible, covalent modification of the enzyme will be exploited to provide heavy-atom labels for the crystallographic structure determination. The crystal structure will be solved by use of anomalous dispersion due to heavy-atoms incorporated in the inhibitor compounds. Very strongly diffracting crystals of the subject enzyme indicate that the structure determination can proceed to very high resolution. Accordingly, crystallographic studies at ultra-low temperature will be pursued in order to define structural details to the fullest extent possible. The results of the structure determination are expected to explain the enzyme's high degree of specificity for substrate acyl, to verify that a single active site is responsible for catalysis of the two enzymatic reactions, to point out possible similarities to other proteins that bind hydrophobic molecules, and to provide additional data on atomic mobility in protein molecules.