State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei Province 430072, China.
Dev Comp Immunol. 2012 Jan;36(1):241-6. doi: 10.1016/j.dci.2011.06.014. Epub 2011 Jul 3.
Three goose-type (g-type) lysozymes, designated as OHLysG1, OHLysG2 and OHLysG3 were identified from expressed sequence tags (ESTs) of a gastropod Oncomelania hupensis, the intermediate host of Schistosoma japonicum. The full cDNA sequences of OHLysG1, OHLysG2 and OHLysG3 consisted of 735, 909 and 808 nucleotides, with an open reading frame of 198, 214 and 249 codons containing a 21, 7 and 8 amino acid (aa) signal peptide at the N-terminus, respectively. The three g-type lysozymes shared conserved features with other g-type lysozymes, such as the substrate binding sites, the catalytic residues critical for the fundamental structure and function of g-type lysozymes. It seems possible that g-type lysozymes in molluscs shared one conserved cysteine with those in birds and mammals, and six conserved cysteines were observed for mollusc g-type lysozymes, with two unique cysteines present in the g-type lysozymes of O. hupensis. The three lysozyme genes were expressed mainly in hepatopancreas, with relatively low expression level observed in head-foot muscle and intestine. When comparing S. japonicum-infected and uninfected snails, significant increase (P<0.05) was observed for all the three lysozymes in infected snails, with the highest increase detected in hepatopancreas, and lowest in intestine, implying their defensive role in the host-parasite, i.e. snail-trematode system. The three recombinant lysozymes expressed in Escherichia coli strain M15 showed lytic activity against Aeromonas hydrophila, Vibrio fluvialis, Aeromonas sobria and Micrococcus lysodeikticus. In conclusion, the finding of three g-type lysozymes in O. hupensis provides structural and functional evidence of multiple g-type lysozymes in gastropod, which may have evolutional implication in the snail-trematode system.
从日本血吸虫中间宿主湖北钉螺的表达序列标签（EST）中鉴定出三种鹅型（g 型）溶菌酶，分别命名为 OHLysG1、OHLysG2 和 OHLysG3。OHLysG1、OHLysG2 和 OHLysG3 的全长 cDNA 序列分别由 735、909 和 808 个核苷酸组成，开放阅读框分别包含 198、214 和 249 个密码子，在 N 端分别含有 21、7 和 8 个氨基酸（aa）的信号肽。这三种 g 型溶菌酶与其他 g 型溶菌酶具有保守特征，如底物结合位点、对 g 型溶菌酶基本结构和功能至关重要的催化残基。似乎贝类中的 g 型溶菌酶与鸟类和哺乳动物中的 g 型溶菌酶共享一个保守的半胱氨酸，并且在贝类 g 型溶菌酶中观察到六个保守的半胱氨酸，在湖北钉螺的 g 型溶菌酶中存在两个独特的半胱氨酸。这三个溶菌酶基因主要在肝胰腺中表达，在头足肌和肠中表达水平较低。在比较感染和未感染日本血吸虫的钉螺时，所有三种溶菌酶在感染钉螺中的表达均显著增加（P<0.05），在肝胰腺中增加最明显，在肠中最低，表明它们在宿主-寄生虫，即钉螺-吸虫系统中具有防御作用。在大肠杆菌 M15 菌株中表达的三种重组溶菌酶对嗜水气单胞菌、弗氏柠檬酸杆菌、温和气单胞菌和微球菌溶菌酶表现出溶菌活性。总之，在湖北钉螺中发现三种 g 型溶菌酶为贝类中存在多种 g 型溶菌酶提供了结构和功能证据，这可能对钉螺-吸虫系统具有进化意义。
