假蜜环菌黄曲霉毒素氧化酶的基因克隆、表达、纯化及酶学性质分析

【目的】黄曲霉毒素氧化酶(aflatoxin-oxidase,AFO)来源于假蜜环菌(Armillariella tabescens)的细胞内提取物,具有转化黄曲霉毒素B1(Aflatoxin B1,AFB1)的特性。为更进一步了解该酶的性质,我们克隆了AFO的基因,并进行了重组AFO蛋白的表达、纯化和酶学性质分析。【方法】本研究利用基质辅助激光解吸飞行时间质谱(MALDI-TOF-MS)获得的AFO短肽序列设计简并引物进行逆转录,再通过cDNA末端快速扩增(rapid-amplification of cDNA ends,RACE)技术获得了AFO基因的全长cDNA序列。构建重组表达载体pPIC9-afo,在毕赤酵母中进行重组AFO(rAFO)的融合分泌表达,用Ni离子螯合层析进行rAFO的纯化,获得有活性的rAFO后,对其进行肽质量指纹(peptide mass fingerprinting,PMF)鉴定和酶学性质分析。【结果】黄曲霉毒素氧化酶(AFO)基因的开放阅读框为2088 bp,编码695个氨基酸;肽质量指纹鉴定结果显示重组AFO的肽片段序列覆盖率为63.2%。活性测定表明纯化后的重组AFO(rAFO)比活力为234 U/mg;对rAFO进行酶学性质分析表明,对于底物黄曲霉毒素B1,rAFO的Km值为3.93±0.20×10-6 mol/L;反应最适温度为30℃,最适pH为6.0;30℃放置90 min后酶活力下降50%;rAFO在pH5.5-7.0之间酶活力较稳定,相对活力维持在51%-65%之间。【结论】本文第一次成功克隆并重组表达了一种具有黄曲霉毒素B1转化功能的酶——黄曲霉毒素氧化酶(aflatoxin-oxidase,AFO),纯化后的重组AFO(rAFO)具有较好的黄曲霉毒素B1转化活性,为进一步研究和应用奠定了基础。

Cloning, expression, purification and characterization of an aflatoxin-converting enzyme from Armillaria tabescens

Objective] Aflatoxin B1(AFB1) is extremely mutagenic,toxic and a potent carcinogen both to humans and livestock.Aflatoxin-oxidase(AFO) was an aflatoxin-converting enzyme previously purified by us from Armillaria tabescens.In order to know better about the molecular characterization of this distinct enzyme,we expressed,purified and characterized the His6 tag fused aflatoxin-oxidase.Methods] Based on sequences of peptides fragments of AFO previously obtained by Electrophoresis-Electrospray Ionization tandem...