中华大蟾蜍色氨酸羟化酶BbgTPH1基因的克隆、原核表达及功能鉴定

Cloning, prokaryotic expression and function of the Bufo bufo gargarizans tryptophan hydroxylase I gene

色氨酸羟化酶(tryptophan hydroxylase I,TPH1)是催化色氨酸生成5-羟色胺的限速酶,而5-羟色胺不仅是蟾酥的主要活性成分,同时也是中枢神经系统重要的神经递质,具有重要的生理功能。本研究从中华大蟾蜍耳后腺文库中克隆得到中华大蟾蜍色氨酸羟化酶c DNA。构建原核重组融合表达质粒p MAL-Bbg TPH1,将其导入Escherichia coli TB1中,用IPTG诱导重组菌并优化诱导表达条件。以色氨酸为底物进行体外酶促反应,采用LC-MS法鉴定反应产物。结果显示Bbg TPH1基因c DNA全长为1 984 bp,开放阅读框1 443 bp,编码480个氨基酸,推测蛋白质分子质量为55.2 k Da,理论等电点为5.58,具有芳香族类羟化酶超基因家族的保守结构域和芳香族类羟化酶家族特有的特征信号序列。氨基酸比对分析表明,该基因编码的氨基酸与其他物种TPH1蛋白序列具有较高的同源性。系统进化树显示Bbg TPH1与非洲爪蟾的TPH1亲缘关系最近。Bbg TPH1在E.coli TB1中能够高效表达,其优化表达条件为诱导温度20℃、IPTG浓度0.5 mmol·L-1。酶活检测结果显示,重组Bbg TPH1具有较高催化活性,可将色氨酸转化为5-羟色氨酸。本研究首次获得了蟾蜍属动物色氨酸羟化酶全长c DNA序列,并验证了其催化功能,为进一步研究蟾蜍中蟾毒色胺类化合物的生物合成分子机制以及次生代谢调控等提供了科学依据。

Tryptophan hydroxylase I（TPH1） catalases the 5-hydroxylation reaction of L-Trp, which is the rate-limiting step in the synthesis of serotonin. Serotonin, a major component of Bufonis venenum, is involved in numerous physiological functions as an important neurotransmitter. In this study, Bbg TPH1 c DNA was cloned from the parotid gland of Bufo bufo gargarizans. Genetic engineering techniques were used to construct a recombinant prokaryotic fusion expression plasmid p MAL-Bbg TPH1, and the induced conditions to express the recombinant Bbg TPH1 in E. coli TB1 cells were optimized. The full length of Bbg TPH1 is 1 984 bp（Gen Bank accession No. JQ768313） with a 1 443 bp open reading frame（ORF） encoding a 480 amino acid residues. The deduced protein molecular weight is 55.2 k Da and its theoretical isoelectric point is 5.58. The sequence includes conserved domain and special signal sequence of the aromatic amino acid hydroxylase（AAAH） superfamily. Homologous alignment showed that Bbg TPH1 shared a high homology with other species. Phylogenetic tree showed the closest relative to Bbg TPH1 was Xenopus tropical-TPH1. The best induction conditions of recombinant Bbg TPH1 were 0.5 mmol·L^-1 IPTG at 20 ℃ for 8 h. The function of Bbg TPH1 was identified by in vitro enzymatic reaction and the recombinant Bbg TPH1 was able to produce 5-hydroxytryptophan by catalyzing tryptophan. This study represents the first time of cloning and identification of the function of TPH1 in Bufo genus. The results of this study will be an important foundation for future studies of biosynthesis of bufotenines in the parotid gland of B. bufo gargarizans.