Lobanov Alexey V, Hatfield Dolph L, Gladyshev Vadim N
Department of Biochemistry, University of Nebraska, Lincoln, Nebraska 68588, USA.
Protein Sci. 2008 Jan;17(1):176-82. doi: 10.1110/ps.073261508.
Proteins containing the 21st amino acid, selenocysteine (Sec), have been described in all three domains of life, but the composition of selenoproteomes in organisms varies significantly. Here, we report that aquatic arthropods possess many selenoproteins also detected in other animals and unicellular eukaryotes, and that most of these proteins were either lost or replaced with cysteine-containing homologs in insects. As a result of this selective selenoproteome reduction, fruit flies and mosquitoes have three known selenoproteins, and the honeybee, Apis mellifera, a single detected candidate selenoprotein. Moreover, we identified the red flour beetle, Tribolium castaneum, and the silkworm, Bombyx mori, as the first animals that lack any Sec-containing proteins. These insects also lost the Sec biosynthesis and insertion machinery, but selenophosphate synthetase 1 (SPS1), an enzyme previously implicated in Sec biosynthesis, is present in all insects, including T. castaneum and B. mori. These data indicate that SPS1 functions in a pathway unrelated to selenoprotein synthesis. Since SPS1 evolved from a protein that utilizes selenium for Sec biosynthesis, an attractive possibility is that SPS1 may define a new pathway of selenium utilization in animals.
含有第21种氨基酸——硒代半胱氨酸（Sec）的蛋白质已在生命的所有三个域中被发现，但生物体中硒蛋白组的组成差异很大。在此，我们报告水生节肢动物拥有许多在其他动物和单细胞真核生物中也能检测到的硒蛋白，并且这些蛋白质中的大多数在昆虫中要么丢失，要么被含半胱氨酸的同源物所取代。由于这种选择性的硒蛋白组减少，果蝇和蚊子有三种已知的硒蛋白，而蜜蜂（意大利蜜蜂）只有一种检测到的候选硒蛋白。此外，我们鉴定出赤拟谷盗和家蚕是首批缺乏任何含Sec蛋白质的动物。这些昆虫也失去了Sec生物合成和插入机制，但硒代磷酸合成酶1（SPS1），一种先前与Sec生物合成有关的酶，存在于所有昆虫中，包括赤拟谷盗和家蚕。这些数据表明SPS1在一条与硒蛋白合成无关的途径中发挥作用。由于SPS1是从一种利用硒进行Sec生物合成的蛋白质进化而来，一种诱人的可能性是SPS1可能定义了动物中硒利用的一条新途径。
