LbCas12a蛋白的原核表达及活性检测

【目的】获得具有体外切割活性的来自毛螺旋菌属(Lachnospiraceae)ND2006的LbCas12a蛋白,以期为LbCas12a的应用研究提供重要的生物学工具。【方法】根据pMBP-LbCas12a质粒(Addgene,113431)的基因序列合成LbCas12a基因,并将其与pET-28a(+)线性化载体进行同源重组,构建重组质粒pET28a-LbCas12a,经测序和NheⅠ、SalⅠ双酶切鉴定后将阳性重组质粒转入大肠杆菌BL21(DE3)感受态细胞中进行IPTG诱导表达。通过12%SDS-PAGE凝胶电泳检测确定IPTG诱导的最佳浓度及温度,鉴定重组蛋白的表达形式,通过Ni-NTA树脂亲和层析的方法进行纯化、超滤法浓缩,BCA法检测蛋白浓度。将浓缩后的LbCas12a与猪细小病毒(PPV)靶标DNA、CRISPR RNA(crRNA)及偶联荧光基团的非特异性单链DNA(ssDNA)探针FQ共孵育,设置1个无LbCas12a蛋白的对照组、4个不同蛋白浓度(125、250、500、1000 nmol/L)的试验组,检测不同组别ssDNA探针的荧光强度,检测测试位点PPV活性。【结果】测序和NheⅠ、SalⅠ双酶切鉴定结果表明,重组质粒pET28a-LbCas12a构建成功且无移码突变。12%SDS-PAGE凝胶电泳检测结果表明,IPTG诱导表达的最佳浓度为0.5 mmol/L,最佳温度为37℃,表达形式主要为可溶性表达。蛋白浓度检测结果表明,浓缩后的蛋白浓度为485 ng/μL,质量为143 ku。活性检测结果表明,125、250、500、1000 nmol/L LbCas12a蛋白组的荧光强度均极显著高于对照组(P<0.01)。【结论】本研究成功表达出高活性的LbCas12a蛋白,且LbCas12a蛋白具有体外切割ssDNA的反式活性,为后续基于CRISPR-LbCas12a系统的分子检测技术奠定了基础。

非洲猪瘟病毒RAA-CRISPR/LbCas12a检测方法的建立与初步应用

本研究基于重组酶介导的扩增技术(recombinase-aid amplification,RAA),联合CRISPR/LbCas12a检测方法,筛选crRNA引物,对不同浓度阳性质粒、其他猪病病毒核酸样品、病料样品进行RAA扩增,随后进行荧光检测,探索检测ASFV的新方法。结果显示,RAA-CRISPR/LbCas12a检测方法的灵敏度达1×103copies/μL,不与其他病毒核酸样品产生交叉反应。利用RAA-CRISPR/LbCas12a方法对22份灭活的猪组织病料进行临床ASFV检测,同时进行qPCR平行检测。结果显示,两种方法的检测结果相同,同时检出18份阳性。综上所述,本研究建立的ASFV RAA-CRISPR/LbCas12a检测方法具有较好的敏感性和特异性,能够在1 h内对ASFV核酸进行判定,且较为方便,在临床ASFV检测中有着一定的应用前景,对于预防非洲猪瘟有一定的推动作用。

A field-deployable method for single and multiplex detection of DNA or RNA from pathogens using Cas12 and Cas13

For some Cas nucleases,trans-cleavage activity triggered by CRISPR/Cas-mediated cis-cleavage upon target nucleic acid recognition has been explored for diagnostic detection.Portable single and multiplex nucleic acid-based detection is needed for crop pathogen management in agriculture.Here,we harnessed and characterized RfxCas13d as an additional CRISPR/Cas nucleic acid detection tool.We systematically characterized AsCas12a,LbCas12a,LwaCas13a,and RfxCas13d combined with isothermal amplification to develop a CRISPR/Cas nucleic acid-based tool for single or multiplex pathogen detection.Our data indicated that sufficient detection sensitivity was achieved with just a few copies of DNA/RNA targets as input.Using this tool,we successfully detected DNA from Fusarium graminearum and Fusarium verticillioides and RNA from rice black-streaked dwarf virus in crude extracts prepared in the field.Our method,from sample preparation to result readout,could be rapidly and easily deployed in the field.This system could be extended to other crop pathogens,including those that currently lack a detection method and have metabolite profiles that make detection challenging.This nucleic acid detection system could also be used for single-nucleotide polymorphism genotyping,transgene detection,and qualitative detection of gene expression in the field.