魁蚶C型凝集素基因cDNA的克隆及表达分析

摘要

The current study cloned the full-length cDNA of C-type lectin (Sb-Lec1) using RACE (Rapid amplification of cDNA ends)method from Scapharca broughtonii with 700 bp that includes a 5′UTR of 29 bp and 3′ UTR of 167 bp. The 504 bp open reading frame (ORF) encodes a polypeptide of 167 amino acids, including a signal peptide of 23 amino acids, one carbohydrate-recognition domain (CRD) motif of 129 amino acids and 6 cysteines involved in the formation of disulfide bond. The predicted protein molecular weight is 19.11 kDa, with a theory isoelectric point of 4.74. Multiple sequences alignment and phylogeny analysis showed that the identity of Sb-Lec1 gene shared with Crassostrea gigas, Mytilus galloprovincialis, and Argopecten irradians was 38%~40%, 34%~35%, and 38%~39%, respectively. The amino acids of CRD motif had many similarities with other species such as 4 conserved Cys. Phylogenetic analysis revealed two main branches including all C-type lectin of molluscs and the C-type lectin of vertebrate, and that the deduced polypeptide of Sb-Lec1 had the characteristics of the C-type lectin family. Quantitative real-time PCR (qRT-PCR) was used to assess the mRNA expression in all tested tissues, including hemocytes, foot, adductor muscle, mantle, gill, and hepatopancreas. The highest and lowest Sb-Lec1 mRNA were in hepatopancreas and adductor muscle,respectively.Vibrio anguillarum challange induced Sb-Lec1 mRNA expression in all tested tissues (P<0.05). These results showed that Sb-Lec1 gene may play an important role in immune defense.%通过 cDNA 末端快速扩增(Rapid amplification of cDNA ends,RACE)技术克隆得到魁蚶(Scapharca broughtonii)C型凝集素(C-type lectin,Sb-Lec1)基因,该基因全长为700 bp,其中,5′-UTR为29 bp,3′-UTR为167 bp,开放阅读框长度为504 bp,编码167个氨基酸,包括长度为23个氨基酸的信号肽序列、129个氨基酸的糖识别结构域(CRD)以及参与二硫键形成的6个半胱氨酸.预测蛋白分子量为19.11 kDa,理论等电点为4.74.多序列比对结果显示,Sb-Lec1基因CRD编码的氨基酸序列与长牡蛎(Crassostrea gigas)、紫贻贝(Mytilus galloprovincialis)和海湾扇贝(Argopecten irradians)C型凝集素的同源性分别为38%~40%、34%~35%和38%~39%,Sb-Lec1基因编码的氨基酸序列与其他物种的凝集素基因具有相似的结构,均含有形成二硫键的4个保守半胱氨酸.系统进化分析结果显示,魁蚶先与贝类聚为一支,再与脊椎动物聚在一起,表明魁蚶Sb-Lec1基因在进化树上的位置与其传统分类所处位置一致.采用荧光定量PCR技术,检测了Sb-Lec1基因在组织中的表达情况,发现其在肝胰腺、血淋巴、鳃、外套膜、闭壳肌、斧足中均有表达,其中,肝胰腺表达量最高.同时,分析了Sb-Lec1基因在鳗弧菌(Vibrio anguillarum)刺激下的mRNA表达量变化情况.结果显示,与对照组相比,菌刺激组Sb-Lec1基因mRNA在各检测组织中的表达量均显著上调(P<0.05),随着刺激时间的延长,表达量呈先升高后降低的趋势.本研究表明,魁蚶Sb-Lec1基因在机体免疫防御方面发挥重要功能.