一种淀粉普鲁兰酶突变体及其应用

文档序号:25424861发布日期:2021-06-11 21:38阅读:128来源:国知局
本发明涉及一种淀粉普鲁兰酶(amylopullulanase,apu)突变体及其应用,属于基因工程和酶工程领域。
背景技术
::环糊精是一系列以α-1,4-糖苷键相连的、环状葡聚糖的总称,以含有6、7、8个葡萄糖单元的α-、β-和γ-环糊精为最常见。由于环糊精的外缘亲水而内腔疏水,所以它能作为主体包络各种适当的客体,形成复合物,从而广泛应用于食品、医药、化工、环保等领域。环糊精葡萄糖基转移酶(cyclomaltodextringlucanotransferase,cgtase)能够催化淀粉中的直链淀粉水解环化、合成环糊精。然而,普通淀粉仅含有20-25%的直链淀粉,大部分为75-80%的支链淀粉。支链淀粉是多个α-1,4-葡萄糖残基组成的线性链被多个α-1,6-糖苷键连接而成的分支多糖。由于环糊精葡萄糖基转移酶不能水解α-1,6-糖苷键,所以淀粉转化为环糊精的产率较低。普鲁兰酶能水解支链淀粉中的α-1,6-糖苷键、脱除支链而产生线性麦芽糊精,所以在生产环糊精的过程中需要同时添加环糊精葡萄糖基转移酶和普鲁兰酶,进而提高环糊精的产率。在工业生产中,传统的环糊精的生产方法为先将淀粉乳加热至90℃以上的高温进行糊化液化,然后降低温度至30-45℃、再加入普鲁兰酶和环糊精葡萄糖基转移酶。这种工艺需要额外增加降温步骤,而且在中等温度下合成环糊精也容易被微生物污染,影响环糊精的产率。随着基因工程和酶工程技术的发展,已经筛选出具有85℃以上的最适催化反应温度的超嗜热环糊精葡萄糖基转移酶和超嗜热淀粉普鲁兰酶,这样,淀粉乳经高温糊化后,不需要降温,就可以直接加入超嗜热环糊精葡萄糖基转移酶和超嗜热淀粉普鲁兰酶进行高温催化。这种工艺不但减少了降温步骤,而且由于在较高的温度下进行催化反应,也不会被微生物污染。但是,现有技术中大多数超嗜热淀粉普鲁兰酶的活性低、专一性差等缺点,影响了环糊精的产率。来源于古细菌staphylothermusmarinusf1的淀粉普鲁兰酶smapu,具有105℃的最适催化反应温度,并且在85-90℃保温3小时,仍能保留90%以上的原始酶活,是目前为止热稳定性最高的超嗜热淀粉普鲁兰酶。它能够在高温催化支链淀粉的脱支反应,直接将普通谷物淀粉转化为线性麦芽糊精。但是,淀粉普鲁兰酶smapu除了具有催化淀粉脱支的活性,还具有将环糊精水解为葡萄糖和麦芽糖的活性。因此,为提高环糊精的产率,降低淀粉普鲁兰酶smapu对环糊精的水解作用是亟待解决的问题。技术实现要素:为了解决上述技术问题,本发明提供了一种淀粉普鲁兰酶突变体及其在制备环糊精中的应用,通过定点突变的方法,使来源于古细菌staphylothermusmarinusf1的淀粉普鲁兰酶smapu不具备环糊精水解活性,提高环糊精的产率。本发明的第一个目的是提供一种淀粉普鲁兰酶突变体,所述淀粉普鲁兰酶突变体是以如seqidno.1所示的氨基酸序列的野生型古细菌staphylothermusmarinusf1淀粉普鲁兰酶smapu为基础,将位于第395位的苯丙氨酸或者位于第510位的苯丙氨酸进行突变得到的。作为本发明的优选,所述突变体是将第395位的苯丙氨酸突变为丙氨酸,命名为smapu-f395a,其氨基酸序列如seqidno.2所示。作为本发明的优选,所述突变体是将所述第510位的苯丙氨酸突变为丙氨酸,命名为smapu-f510a,其氨基酸序列如seqidno.3所示。本发明还提供了携带上述基因或者上述表达载体的微生物细胞。本发明的最后一个目的是提供一种制备环糊精的方法,所述方法为将上述淀粉普鲁兰酶突变体与环糊精葡萄糖基转移酶添加至含有淀粉乳的反应体系中进行酶解,从反应液中分离得到环糊精。作为本发明的优选,所述淀粉普鲁兰酶突变体在反应体系中的加酶量为4-10u/g淀粉,所述反应体系中淀粉的浓度为100-350g/l,所述环糊精葡萄糖基转移酶的加酶量为2.5-5.0u/g淀粉,反应的ph为4.0-7.0,反应温度为70-100℃。本发明的淀粉普鲁兰酶突变体具有水解支链淀粉中的α-1,6-糖苷键的活性的同时,完全丧失了水解环糊精活性,在淀粉、环糊精葡萄糖基转移酶的高温反应体系中,加入本发明的淀粉普鲁兰酶突变体,可以使环糊精的总产率较使用突变前的野生型古细菌staphylothermusmarinusf1淀粉普鲁兰酶smapu制备环糊精的总产率提高43%以上。附图说明附图1为淀粉普鲁兰酶smapu、淀粉普鲁兰酶突变体smapu-f395a和smapu-f395a的十二烷基硫酸钠聚丙烯酰胺凝胶电泳图。具体实施方式以下实施例中,未注明具体条件的,均按常规条件或制造商建议的条件进行,除非特殊说明,否则所述百分比为重量体积比。实施例1:淀粉普鲁兰酶smapu突变体重组菌的构建根据来自古细菌staphylothermusmarinusf1的淀粉普鲁兰酶smapu基因信息,构建携带有如seqidno.4所示的淀粉普鲁兰酶smapu基因的表达载体psmapu6xh(表达载体psmapu6xh的构建方法记载于文献lix,lid,parkkh.anextremelythermostableamylopullulanasefromstaphylothermusmarinusdisplaysbothpullulan-andcyclodextrin-degradingactivities.applmicrobiolbiotechnol.2013jun;97(12):5359-69.)利用全质粒pcr技术,以上述含有淀粉普鲁兰酶smapu基因的psmapu6xh重组质粒为模板,进行定点突变,获得突变体重组质粒及突变体重组菌。其中,淀粉普鲁兰酶突变体smapu-f395a是通过将淀粉普鲁兰酶smapu(seqidno.1)的第395位苯丙氨酸突变为丙氨酸得到,氨基酸序列如seqidno.2所示,所用引物如下:正向引物:ggagaaaactggatgtcagcttcagttaatccaccgtta;反向引物:taacggtggattaactgaagctgacatccagttttctcc。淀粉普鲁兰酶突变体smapu-f510a是通过将淀粉普鲁兰酶smapu(seqidno.1)的第510位苯丙氨酸突变为丙氨酸得到,氨基酸序列如seqidno.3所示,所用引物如下:正向引物:gattactggtgggcagaggcgtggttacctaaaataata;反向引物:tattattttaggtaaccagcgctctgcccaccagtaatc。聚合酶链式反应体系(pcr)均为:5×psbuffer10μl,dntpsmix(2.5mm)4μl,正向引物(10μm)1μl,反向引物(10μm)1μl,模板dna(psmapu6xh)1μl,primestarhs(2.5u/μl)0.5μl,加入灭菌双蒸水至50μl。pcr扩增条件为:98℃预变性30s;随后20个循环(98℃10s,55℃15s,72℃5min);72℃继续延伸10min。取47μl上述pcr反应液中,加入2μl限制性内切酶dpni(10u/μl),在37℃保温1h后,取3μl混入100μl大肠杆菌mc061感受态细胞,在冰上放置20min以后,于42℃热激1min,再加入700μllb液体培养基、在37℃保温1h后,涂布于含40μg/ml卡那霉素的lb固体培养基平板,在37℃过夜培养,挑取阳性克隆接种至含40μg/ml卡那霉素的lb液体培养基中培养8h后,提取质粒并测序,测序正确即为:携带突变体f395a和f510a基因的质粒psmapu6xh-f395a和psmapu6xh-f510a;相应的重组菌株为mc1061/psmapu6xh-f395a和mc1061/psmapu6xh-f510a。实施例2:淀粉普鲁兰酶smapu突变体的制备与分析分别将实施例1得到的重组菌株mc1061/psmapu6xh-f395a和mc1061/psmapu6xh-f510a划线于含40μg/ml卡那霉素的lb固体培养基(1%w/v胰蛋白胨,0.5%w/v酵母提取物,1%w/v氯化钠,1.5%w/v琼脂)平板,在37℃过夜培养,再分别挑取单菌落接种于含40μg/ml卡那霉素的lb液体培养基(1%w/v胰蛋白胨,0.5%w/v酵母提取物,1%w/v氯化钠),在37℃、250rpm的摇床中继续培养20h;将重组菌培养液于7000g离心20min,用1/10发酵液体积的裂解缓冲液(50mph7.4tris-hcl,500mmnacl,5mm咪唑)重悬菌体、将50ml菌体用超声波(750w,35%振幅,15min)破碎,于9000g离心20min,将得到的细胞提取酶液放在50ml离心管,于70℃的水浴中处理15min,于9000g离心20min,再将热处理后的酶液通过ni离子-葡聚糖亲和色谱柱,用洗脱缓冲液(tris-hcl50mph7.4,氯化钠500mm,咪唑500mm)解析,再装入半透膜在缓冲液(tris-hcl50mph7.4)中透析除去氯化钠和咪唑,而最终得到纯化的淀粉普鲁兰酶突变体smapu-f395a和smapu-f510a。酶活力的测定:取150μl1%普鲁兰溶液或者1%γ-环糊精溶液,加入75μl200mmol/lph5.0醋酸-醋酸钠缓冲液,混匀后,在90℃,预热3min后,再加入75μl淀粉普鲁兰酶smapu或者淀粉普鲁兰酶突变体smapu-f395a或者淀粉普鲁兰酶突变体smapu-f510a,继续在90℃保温10min,立即加入900μl3,5-二硝基水扬酸溶液终止反应,放入沸水浴中煮5min,冷却到室温后,用分光光度计在575nm测定吸光度。根据麦芽糖标准曲线,计算出麦芽糖浓度。将每分钟产生1μmol麦芽糖所需要的酶量定义为一个单位酶活力(1u)。酶蛋白质含量的测定:取100ul适当稀释的淀粉普鲁兰酶smapu或者淀粉普鲁兰酶突变体smapu-f395a或者淀粉普鲁兰酶突变体smapu-f510a的溶液置于1.5ml的离心管中,加入900μl的考马斯亮蓝染液(将100mg考马斯亮蓝g-250溶于50ml95%乙醇,加入100ml85%的磷酸;然后用蒸馏水补充至1000ml)混匀,用分光光度计在595nm测定吸光度。根据牛血清白蛋白标准曲线,计算出酶液中的蛋白质浓度。酶的比活力=酶活力单位(u)/酶蛋白质含量(mg)酶促反应动力学参数的测定:在90℃,ph5.0(50mm乙酸钠缓冲液),过量淀粉普鲁兰酶smapu或者淀粉普鲁兰酶突变体smapu-f395a或者淀粉普鲁兰酶突变体smapu-f510a催化不同浓度普鲁兰或者γ-环糊精的反应中,于30、60、90、120、150和180s,取50μl反应液,立即加入等体积的0.1mhcl停止反应,再加入等体积的0.1m氢氧化钠中和,然后加入150μl铜二喹啉,在80℃保温35min后,用分光光度计在510nm测定吸光度。根据麦芽糖标准曲线,计算出麦芽糖浓度。以底物浓度的倒数和反应速度的倒数做lineweaver-burk图,曲线与x轴截距的倒数的负数即为米氏(michaelis-menten)常数km,曲线与y轴截距的倒数即为最大反应速度vmax,最大反应速度除以酶浓度即为转换数kcat。淀粉普鲁兰酶smapu及淀粉普鲁兰酶突变体smapu-f395a和smapu-f510a水解普鲁兰及γ-环糊精的米氏常数km、转换数kcat、催化效率kcat/km及比活力的实验结果如表1所示:表1淀粉普鲁兰酶smapu和突变体的酶促反应动力学参数和比活力由表1结果可以得出,与淀粉普鲁兰酶smapu相比,淀粉普鲁兰酶突变体smapu-f395a和smapu-f510a在具备水解普鲁兰活性的前提下,完全丧失了水解γ-环糊精的活性。实施例3:淀粉普鲁兰酶突变体与环糊精葡萄糖基转移酶联合催化淀粉水解合成环糊精取300g玉米淀粉,加入1l去离子水中,搅拌加热至95℃后,分别加入2100u纯化后淀粉普鲁兰酶突变体smapu-f395a或者淀粉普鲁兰酶突变体smapu-f510a,和960u的环糊精葡萄糖基转移酶thermococcussp.b1001cgtase(tscgtase,制备方法记载于文献yamamotot,fujiwaras,tachibanay,takagim,fukuik,imanakat.alterationofproductspecificityofcyclodextringlucanotransferasefromthermococcussp.b1001bysite-directedmutagenesis.jbioscibioeng.2000,89(2):206-9.),继续在95℃保温24hr。环糊精的测定:将50μl上述反应混合物与9μl乙酸钠缓冲液(2m,ph5.0)混合,并加入1u淀粉葡萄糖苷酶(amyloglucosidasefromaspergillusniger,a1602,sigma-aldrich),在50℃下孵育60min后,加入150μl乙腈,再用孔径为0.45μm的滤膜过滤。吸取过滤液20μl,进行高效液相色谱(hplc)分析。hplc条件为;ymc-packpolyamineii色谱柱(250×4.6mmi.d.;京都,日本),示差检测器(流通池30℃),乙腈-水(75:25v/v)流动相,流速1.0ml/min。将得到的α-环糊精、β-环糊精、γ-环糊精hplc峰面积,代入环糊精标准曲线,从而得到相应环糊精的浓度,再除以淀粉的初始浓度,即得到相应环糊精的产率,以百分数表示。对比实施例1:环糊精葡萄糖基转移酶催化淀粉水解合成环糊精本对比实施例的方法包括实施例3中的大部分技术方案,其区别在于只添加960u的环糊精葡萄糖基转移酶tscgtase,不添加淀粉普鲁兰酶突变体。对比实施例2:淀粉普鲁兰酶与环糊精葡萄糖基转移酶联合催化淀粉水解合成环糊精本对比实施例的方法包括实施例3中的大部分技术方案,其区别在于不添加淀粉普鲁兰酶突变体,而是添加淀粉普鲁兰酶smapu。实施例3、对比实施例1和对比实施例2中所制得的环糊精产率的具体结果如表2所示:表2不同酶催化淀粉所得环糊精的产率由表2结果可以得出,本发明的普鲁兰酶突变体smapu-f395a和smapu-f510a与环糊精葡萄糖基转移酶tscgtase联合催化淀粉生产环糊精的产率都有明显的提高,分别比只添加环糊精葡萄糖基转移酶tscgtase的环糊精产率提高了105.4%和108.4%,分别比添加普鲁兰酶smapu和环糊精葡萄糖基转移酶tscgtase的环糊精产率提高了43.7%和45.8%。本发明的普鲁兰酶突变体smapu-f395a和smapu-f510a在工业生产环糊精的过程中具有应用潜力。以上实施例仅用以说明发明的技术方案,而非对其限制;尽管参照前述实施例对本发明进行了详细的说明,本领域的普通技术人员应当理解:其依然可以对前述各实施例所记载的技术方案进行修改,或者对其中部分技术特征进行等同替换;而这些修改或者替换,并不使相应技术方案的本质脱离本发明各实施例技术方案的精神和范围。序列表<110>长春大学<120>一种淀粉普鲁兰酶突变体及其应用<160>4<210>1<211>639<212>prt<213>古细菌staphylothermusmarinusf1<400>1metgluvalleuasplystyrserserleuilelysprolysleu151015ileasnasnileglualatyrmetvalpheasplysproalahis202530lysproasnalaglualalysiletyrvalleuleuasnasnhis354045glyserargargaspilehistyrlysilevalserileasparg505560asnarggluvalpheserlysargileasnvalaspglulyslys657075pheleuilegluthrileserilegluthrproasplysprogly808590argphecystyrlysleupheileaspasngluglnileaspasn95100105thrcyspheleuvalglyaspproserserarggluglnmettyr110115120phethrilevaltrphishishisglnalaproasntyrleupro125130135aspglyargilehisglyprotrpalatyriletyrvaltrpser140145150aspleuleulysprotyrglylysglyprotyrhistyrhisser155160165valmetleuasnilehisprohisphelysalathrtyrasnleu170175180serproserleuleuargglntrpglnilealavalglulysgly185190195valgluphevalasnglyglulystyraspproasnhisglulys200205210ileargleuvalglugluthrleuasnasntyrargglualaleu215220225phelysglyglnileaspvalleuthrseriletyralahisthr230235240ileglyglypheleuthraspvalleuglyalathrasnileval245250255gluglugluileargtyrglylysgluvalthrserlysilemet260265270glyasnasntyrasnproglnglyiletrpthrproglumetala275280285phesermetlysleuileproiletyrtyraspleuaspilelys290295300tyrthrvalleuaspasplysphehisphephehisalaglugly305310315asnlysaspserglntyrgluprotyrmetvalileaspthrglu320325330serlyslystyrilethrvalphepheargasphisaspleuser335340345aspileleuglypheargasnasnphetyrsergluprohisala350355360trpargasnalatyrgluphealaleuargvalalaglulystrp365370375pheasplysasnvallysvalleuthrilealaleuaspglyglu380385390asntrpmetserpheservalasnproproleuthralatyrphe395400405leuasplysmetileiletyrleugluthrleuseraspasnlys410415420pheilelysleuserthrleuarggluiletyrasnlysvalpro425430435alaasnargileleuthrasnileprothrasnsertrpleugly440445450thrphearglystrpargglygluvalproglnhisgluglutyr455460465trpilelysthrtyrservaltyrarglysleuleualatyrglu470475480glumetileglyglyargaspglupheserasnglualaargtrp485490495alaleutrphisalaleuaspserasptyrtrptrpalagluphe500505510trpleuprolysileileaspthrtrpleuservalalagluasn515520525ileleuasnasnargileasnlysileglnileileaspvalarg530535540proalasergluphetyrgluaspglulysalaglyleuvalval545550555thrileargasnglnleuglulysgluileargvalserpheala560565570ileglyglythrglypheserservalasnasnaspleugluthr575580585vallysmetasnproasnsersertyrthrargileileproval590595600lysalalyspheileglylyshislysmetvalvalseralaile605610615serlysglyleuileileaspserlysileileaspileasnval620625630lysprolysleuleuproasnproarg635<210>2<211>639<212>prt<213>人工合成<400>2metgluvalleuasplystyrserserleuilelysprolysleu151015ileasnasnileglualatyrmetvalpheasplysproalahis202530lysproasnalaglualalysiletyrvalleuleuasnasnhis354045glyserargargaspilehistyrlysilevalserileasparg505560asnarggluvalpheserlysargileasnvalaspglulyslys657075pheleuilegluthrileserilegluthrproasplysprogly808590argphecystyrlysleupheileaspasngluglnileaspasn95100105thrcyspheleuvalglyaspproserserarggluglnmettyr110115120phethrilevaltrphishishisglnalaproasntyrleupro125130135aspglyargilehisglyprotrpalatyriletyrvaltrpser140145150aspleuleulysprotyrglylysglyprotyrhistyrhisser155160165valmetleuasnilehisprohisphelysalathrtyrasnleu170175180serproserleuleuargglntrpglnilealavalglulysgly185190195valgluphevalasnglyglulystyraspproasnhisglulys200205210ileargleuvalglugluthrleuasnasntyrargglualaleu215220225phelysglyglnileaspvalleuthrseriletyralahisthr230235240ileglyglypheleuthraspvalleuglyalathrasnileval245250255gluglugluileargtyrglylysgluvalthrserlysilemet260265270glyasnasntyrasnproglnglyiletrpthrproglumetala275280285phesermetlysleuileproiletyrtyraspleuaspilelys290295300tyrthrvalleuaspasplysphehisphephehisalaglugly305310315asnlysaspserglntyrgluprotyrmetvalileaspthrglu320325330serlyslystyrilethrvalphepheargasphisaspleuser335340345aspileleuglypheargasnasnphetyrsergluprohisala350355360trpargasnalatyrgluphealaleuargvalalaglulystrp365370375pheasplysasnvall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aattatagatgtgaga1620ccagcatctgaattctatgaagacgagaaagcaggcttagttgttacgattagaaaccaa1680ttagagaaagaaatacgtgtatcatttgctataggtggtacgggattttcatctgtaaat1740aatgatcttgaaacagtaaaaatgaaccctaattcgtcatatacaagaataatacctgta1800aaagctaagttcataggcaaacacaaaatggtggtttcagcgatttctaaaggattaatt1860atagatagcaaaatcatcgatataaatgtgaaacctaaactattaccaaatccaagatga1920当前第1页12当前第1页12
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