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The razor clam Sinonovacula constricta uses the strategy of conversion of toxic ammonia to glutamine in response to high environmental ammonia exposure
Molecular Biology Reports ( IF 2.8 ) Pub Date : 2020-11-27 , DOI: 10.1007/s11033-020-06018-w
Huan Zhang , Gaigai Sun , Zhihua Lin , Hanhan Yao , Yinghui Dong

High ammonia can inhibit the survival and growth, and even cause mortality of razor clam (S. constricta). The accumulation of ammonia to lethal concentrations in some invertebrates may be partially prevented by converting some of the ammonia into glutamine (Gln). Glutamine dehydrogenase (GDH) and glutamine synthetase (GS) have been widely implicated a central role in response to ammonia stress. However, the molecular and physiological response of GDH and GS to ammonia alterations has not yet been determined in clams. To investigate the possible participatory role of GDH and GS genes in altered ammonia conditions, we have cloned their gene sequences and examined the mRNA expression and western blotting under ammonia exposure in S. constricta (ScGDH and ScGS), and detected the levels of GS and GDH, and the content of glutamate (Glu) and Gln. The full-length cDNA of ScGDH was 3924 bp, with a 1629 bp open reading frame (ORF) encoding a 542 amino-acid polypeptide. The complete cDNA sequence for ScGS had 2739 bp with an ORF of 1110 bp encoding 369 amino acids. To investigate ammonia detoxification strategies, the clams were exposed to ammonia for 96 h at four different concentrations (0, 100, 140, and 180 mg/L). Exposure to ammonia resulted in a significant increase of glutamate concentration and Gln in the haemocytes. GDH activity, GDH relative mRNA and protein expression, GS activity, GS relative mRNA and protein expression increased significantly and showed a pronounced time and dosage interaction in the liver. The results suggested that the protective strategies of Gln formation existed in S. constricta, which could convert ammonia to non- or less toxic nitrogenous compounds on the exposure of ammonia. Glutamate content in the haemocytes increased significantly, which is to ensure sufficient Glu to meet the needs for GS to catalyze the conversion of ammonia to Gln. We proposed that the induction of Glu synthesis-related genes and the subsequent formation of the active protein occurred in preparation for the increased capacity of the body to convert ammonia, into Gln. The results of this study suggested that GDH and GS play an important role in the synthesis of Gln, emphasizing, the protective strategies of Gln formation in S. constricta convert ammonia to nontoxic or less toxic nitrogenous compounds upon exposure to ammonia.



中文翻译:

剃刀蛤Sino新nova虫采用了将有毒氨转化为谷氨酰胺的策略,以应对高环境氨暴露

高含量的氨会抑制其生存和生长,甚至导致剃刀蛤(S. constricta)死亡。通过将一些氨转化为谷氨酰胺(Gln),可以部分防止氨在某些无脊椎动物中积累至致死浓度。谷氨酰胺脱氢酶(GDH)和谷氨酰胺合成酶(GS)已被广泛认为对氨胁迫有重要作用。然而,在蛤中尚未确定GDH和GS对氨变化的分子和生理反应。为了研究GDHGS基因在改变的氨气条件下的可能参与作用,我们克隆了它们的基因序列,并检查了氨氮暴露在收缩链球菌中的mRNA表达和蛋白质印迹ScGDHScGS),并检测GS和GDH的水平,以及谷氨酸(Glu)和Gln的含量。ScGDH的全长cDNA为3924 bp,具有1629 bp的开放阅读框(ORF),编码542个氨基酸的多肽。ScGS的完整cDNA序列2739 bp,ORF为1110 bp,编码369个氨基酸。为了研究氨的解毒策略,将蛤暴露于四种不同浓度(0、100、140和180 mg / L)的氨中96小时。暴露于氨导致血细胞中谷氨酸盐浓度和Gln显着增加。GDH活性,GDH相对mRNA和蛋白质表达,GS活性,GS相对mRNA和蛋白质表达显着增加,并且在肝脏中显示出明显的时间和剂量相互作用。结果表明,S。constricta中存在Gln形成的保护策略,如果暴露在氨气中,可能会将氨气转化为无毒或毒性较小的含氮化合物。血细胞中的谷氨酸含量显着增加,这是为了确保有足够的Glu满足GS催化氨向Gln转化的需要。我们建议诱导Glu合成相关基因并随后形成活性蛋白,以准备增加人体将氨转化为Gln的能力。这项研究的结果表明,GDH和GS在Gln的合成中起着重要作用,强调在收缩链霉菌中Gln形成的保护策略是将氨暴露于氨后将其转化为无毒或毒性较小的含氮化合物。

更新日期:2020-11-27
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