大口黑鲈G6pc和Gck的原核表达、抗体制备及饲料淀粉水平对其表达的影响

PROKARYOTIC EXPRESSION, ANTIBODY PREPARATION, AND REGULATION BY DIETARY STARCH LEVELS OF G6PC AND GCK IN MICROPTERUS SALMOIDES

  • 摘要: 为深入研究营养因子调控大口黑鲈(Micropterus salmoides)葡萄糖稳态的分子机制, 研究成功克隆并构建了大口黑鲈葡萄糖-6-磷酸酶催化亚基(G6pc)和葡萄糖激酶(Gck)截短序列的重组质粒载体, 转化至Escherichia coli Rosetta感受态细胞并以1 mmol/L IPTG (异丙基-β-D-硫代半乳糖苷)、16℃诱导表达过夜, 在细胞破碎后的上清中得到了大量表达。通过GST-tag亲和层析的方法纯化得到高纯度的G6pc和Gck截短重组蛋白后, 将其分别与弗氏佐剂乳化成免疫原, 免疫KM小鼠5次, 成功制备具有高特异性和高效价的多克隆抗体(G6pc和Gck抗体的效价分别大于1﹕3000和1﹕10000)。Westen blot检测发现大口黑鲈G6pc和Gck蛋白主要分布在肝脏中, 免疫荧光染色显示G6pc的阳性信号定位于细胞核周围, 而Gck的阳性信号散布整个细胞。在8周养殖实验结束后, 随饲料淀粉水平以6%的梯度从8%增加到20%, 大口黑鲈肝脏中糖酵解和糖原合成关键酶编码基因的表达及Gck水平逐渐升高, 但糖异生和糖原分解关键酶编码基因的表达及G6pc水平仅在14%淀粉水平时被抑制, 意味着在高淀粉水平(20%)下大口黑鲈肝脏中葡萄糖-G6P间的相互转化发生了无效循环。综上所述, 研究成功制备了大口黑鲈G6pc和Gck特异性识别的多克隆抗体, 探明了饲料淀粉水平对其表达的影响, 为深入研究G6pc和Gck在大口黑鲈葡萄糖稳态维持过程中的重要作用奠定了基础。

     

    Abstract: The dysregulation of glucose-G6P (glucose-6-phosphate) interconversion is thought to be an important reason for the low glucose tolerance of carnivorous fish. However, it remains unclear if this phenomenon applies to largemouth bass (Micropterus salmoides, LMB). To investigate the regulatory mechanism of glucose homeostasis influenced by nutritional factors in LMB, we cloned and constructed recombinant plasmid vectors containing truncated sequences of glucose-6-phosphatase catalytic subunit (g6pc) and glucokinase (gck). These recombinant plasmid vectors were transformed into Escherichia coli Rosetta receptor cells and successfully expressed using 1 mmol/L IPTG (isopropyl-β-D-thiogalactopyranoside) induction overnight at 16℃. Following the lysis receptor cells, truncated G6pc, and Gck recombinant proteins were purified by GST-tag affinity chromatography from the supernatants. The purified recombinant proteins were emulsified with Freund's adjuvant to create immunogens, and immunized to KM mice for five times. G6pc and Gck polyclonal antibodies with high specificity were successfully prepared with titers exceeding 1﹕3000 and 1﹕10000, respectively. Western blot analysis showed that both G6pc and Gck in LMB were mainly distributed in the liver. Immunofluorescent staining indicated that the G6pc positive signals were localized around the nucleus, whereas Gck positive signals spread throughout the hepatocytes. After an 8-weeks feeding trial, the results showed that Gck level and the expression of genes involved in glycolysis and glycogenesis in the liver of LMB increased gradually with dietary starch levels rising from 8% to 20% in 6% increments. Conversely, G6pc levels and the expression of genes involved in gluconeogenesis and glycogenolysis were only down-regulated at 14% starch. These results suggested that a high starch diet (20%) could induce a futile cycle of glucose-G6P interconversion in the liver of LMB. In summary, specific polyclonal antibodies of G6pc and Gck were successfully prepared in LMB, and the regulation of their expression by dietary starch levels was evaluated in this study. This research lays the foundation for further elucidating the roles of G6pc and Gck in the glucose homeostasis of LMB.

     

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