Study On Selenium Distribution And Selenoproteins Bioinformatics In The Silkworms

Selenium is an essential biological trace element. Excessive or inadequate selenium intake will lead to physiological disorder or diseases. The biological function of selenium is mainly exerted through selenoproteins. The silkworm genome sequencing and annotation have been accomplished in 2004. Since selenocystein, the active center of the selenoprotein, is translated in response to UGA codon (a stop signal in the canonical genetic code), selenoproteins are misannotated or completely lost by general programs of gene prediction. Therefore, new analysis should be carried out for the identification of selenoproteins in the genome. In order to investigate the biological function of selenium in the silkworm, a comprehensive research has been conducted in terms of selenium distribution, and the structure and function of selenoproteins.To screen selenium-rich silkworms and to study the distribution of selenium, 28 kinds of silkworm with different strains, voltinism, moltinism, and stirps were chosen and reared to 5 ages 3 days. Meanwhile, one kind of silkworm (Bombyx mori) was dissected for its head, silk gland, testis, midgutand, fat body and epidermis. The selenium contents were measured by AFS-920 hydride generation atomic fluorescence spectrometry. Results showed that the selenium content in Bombyx mori was 182.8255±0.9840μg/Kg. On selenium distribution in Bombyx mori, its testis contained the highest selenium content and its head took second place. Those results indicate that selenium play important roles in the procreation and nervous system of the silkworm. Different kinds of silkworm have different capacity to enrich selenium. As compared with Bombyx mori, significant differences (P<0.05) occurred in selenium contents of the silkworms of Chinese strain, four-moulter, local stirps and practicable breedings. Among those kinds of silkworm, Chinese strain had the highest capacity to enrich selenium with the selenium content of 214.9334μg/Kg.In order to study the chemical form and biological function of selenium in the silkworm, Bombyx mori, selenoproteomes were identified using bioinformatical method. Results showed that Bombyx mori had five selenoprotein genes annotated previously as GST, CG6024, CG5195, ATP-binding cassette transporter subfamily A (ABCA), and nuclear VCP-like protein. Among them GST has been reported as a microbial selenoprotein, the other four are novel selenoproteins. To confirm the versatility of the method, the new method was also used to investigate the zebra fish genome and found thirteen novel selenoproteins.To infer the biological function of silkworm selenoproteins, a series of software were used to predict the silkworm selenoproteins'structures and domains. Results showed that the selenoproteins of Bmb007600, Bmb016238, Bmb018303, and Bmb014121 mainly hadα-helices andβ-sheets, while the Bmb001751 has a large number of irregular coils. Bmb016238 protein had a transmembrane topology with N-terminus inside membrane and continuously crossing membrane three times. Bmb014121 protein had its N-terminus inside and crossing membrane once. Bmb007600 had its N-terminus outside and crossing membrane once.Bmb016238 had a cleavage site of signal peptide between position 24 and 25. Bmb001751 contained a low-density lipoprotein acceptor domain and a CUB domain. Bmb018303 had unintegrated PEP carboxykinase-like and ATP_GTP_A2 sequences. Bmb014121 included various P-loops containing the fragment of nucleoside triphosphate hydrolases. Bmb016238 contained a leucine-rich repeat. Theses results implicate that the five selenoproteins play important roles in resisting disease and stress, increasing immunity, enhancing procreation and nerve growth, and cell apoptosis.Although the five selenoproteins identified in the silkworm have to be confirmed experimentally, researches in this paper provide a direction and theoretical base for later study on selenium in the silkworm.