Evolution of selenocysteine decoding and the key role of selenophosphate synthetase in the pathway of selenium utilization

Evolution of selenocysteine decoding and the key role of selenophosphate synthetase in the pathway of selenium utilization" (2006). Summary: The complete sequencing of genomes and the development of in silico methods for identification of genes encoding selenocysteine (Sec)-containing proteins have greatly contributed to shape our view on the evolution of selenium utilization in nature. Current evidence is consistent with the idea that Sec decoding is a late addition to the genetic code and it evolved once, before the separation of archaeal, bacterial and eukaryal domains. Many organisms have lost the Sec decoding trait, but recent evidence has shown that the loss is not irreversible. The distribution of organisms that use UGA as a Sec codon suggests that Sec decoding evolved as a result of speciation, differential gene loss and horizontal gene transfer. Selenium is also used in the synthesis 2-selenouridine, a modified base of unknown function located in the wobble position of certain tRNAs. It has been recently demonstrated that selenouridine and Sec-decoding traits can evolve independently of each other, but both require selenophosphate synthetase. This ATP-dependent enzyme emerged as a key feature of selenium utilization that allows separation of selenium from the pathways of 40 Selenium: Its molecular biology and role in human health sulfur utilization and non-specific use of selenium. Some animals, including mammals, evolved two selenophosphate synthetases, highlighting an unknown complexity of selenium utilization in nature. Introduction Co-translational incorporation of selenocysteine (Sec) into nascent polypeptides is neither canonical nor universal. A Sec-decoding apparatus is needed to reprogram specific UGA codons [I-31. The Sec-decoding apparatus and selenoprotein genes are present in the three domains of life; yet, many taxa lack them. In Sec decoding species, the selenoproteome consists of a restricted number of proteins [4,5]. All these observations have raised important questions regarding the evolution of Sec utilization in nature. For example, how and when did the translation machinery to decode Sec evolve? If it evolved once, has it been perpetuated solely by vertical descent? Has the UGA codon evolved from nonsense to sense or vice versa? Have extant selenoproteins evolved from Cys-containing proteins or vice versa? What are the selective forces that result in maintenance, loss and acquisition of the Sec-decoding trait and selenoproteins? In a broader scenario, studies on the evolution of Sec invite more in-depth questions regarding the evolution of the genetic code and the translation machinery. Recent work allowed some of these questions to …