细菌多药外排系统及其研究方法的进展(1).docx

细菌多药外排系统及其研究方法的进展细菌多药外排系统及其研究方法的进展 (1)(1) 【摘要】位于细菌细胞膜上的多药外排泵可将多种结 构无关药物排出，本文综述了细菌主要外排泵包括初级和 次级转运系统的分子生物学特征及外排蛋白结构与药物识 别和转运上的关系；同时总结了对外排蛋白进行结构与功 能关系研究的主要的方法，包括定点诱变、螺旋空间排列 和结晶等 【关键词】细菌外排泵多药耐药 Introduction Theproblemofdrugresistanceisamainobstacleinthestrug glebetweenhumanbeingandinfectiousdiseases.Oneofthem ostimportantbacterialresistantmechanismsisthemultid rugeffluxpumpssituatedonthemembranes,whichcanbeclas sifiedintotwomajortypesbasedontheenergysource:prima rytransportsystem,suchasATPbindingcassettetranspo rtersuperfamilyutilizestheenergyproducedbyATPhydrol ysistoeffluxdiversecompounds;whilesecondarytranspor tsystempumpsdifferentsubstratesviatheprotonmotivefo rceprovidingbytransmembraneelectrochemicalprotongra dient or thesodiummotiveforcesupplyingbyiongradient s.Despitethetotallydifferentevolutionarytraitandene rgysources,bothcantransportabroadspectrumofstructur allyunrelatedsubstrates.Todate,duetothehighlyhydrop hobicnature,thecrystallizationofthestructureonmosto fthemembranetransportersisyettobecrackeddown,albeit recently,afewhavebeenpartiallycrystallized.Therefor e,themostimportantanalysisapproachisstillproteineng ineeringmethodsinvolvingsitedirectedmutagenesisan dchemicalmodification.Andcurrentlytherehavedevelope dsomeimprovementsonthesemethods. Bacterialmultidrugeffluxpumpsystems ATPbindingcassettetransporter Todate,LmrAistheonlywellcharacterisedbacterialo riginABCtransporter,whichisencodedbychromosomallylo catedlmrAgeneinLactococcuslactis.Ingeneral,activeAB Cproteinsdemandminimaltwotransmembranedomainsandtwo ABCunits.Theformerusuallyconsistsofsixtransmembrane segments;thelatter,a200～250aminoacids,containsthre econservedmotifsWalkerA,ABCsignatureandWalkerB.Ther efore,functionalstructuralmoduleis2.Comparingwithfu nctionalABCtransportersuchashumanmultidrugresistanc ePglycoprotein,LmrAhasonlytwodomains,buthomologou stoeachofthetwohalvesofthePgp,suggestingthatitbel ongsto“halfABCtransporter“andfunctionsasahomodimer, whichhasbeenidentifiedbyvariousstudies［1～3］. AlthoughthewidesubstratetransportmechanismofLmrAs tillremainsunclear,twohypotheseshavebeenproposed:hy drophobicvacuumcleanermodelshowsthattoxichydrophobi ccompoundsaredirectlyextrudedfromtheinnerleafletoft hemembraneintotheexternalwaterphase［4］; andtheflippasemodelsuggeststhatLmrAfirstrecognizess ubstratesintheinnerleafletofthemembranethenflipthem totheouterleafletfromwheretheydiffuseintotheexterio r.Possibly,substratebindingresultinginconformatio nalchanges,whichmodulatetheinteractionbetweenNBDsan dATP,triggersthetransport.Thebindingandhydrolysisof ATPbyonesiteleadtothemovementofdrugbindingsitefro minnermembranetotheoutsideduetothepreventionofATPhy drolysisattheothersite,sothedrugscanbetranslocatedb etweenthehighandlowaffinitybindingsites,whichfo rmsatransportcycle［5］. Sofar,theconfirmedsubstratesofLmrAincludeanticancer drugs,DNAintercalators,toxicpeptides,fluorescentmem braneprobesanddyesaswellasclinicallyimportantantibi oticssuchasaminoglycosides,lincosamides,macrolides, quinolones,streptograminsandtetracyclines［6］. Hence,theunusuallybroadantibioticprofileofLmrAandpo ssiblegenetransferoflmrAtootherbacteriaenablethenon pathogenicpotentiallythreatened［7］. SomeotherbacterialABCtransportersarealsoidentified, suchastheDrrABdoxorubicin/daunorubicintransporterof Streptomycesprucetius;theMsbAandBtuCDtransportersof Escherichiacoli,whicheffluxlipidAandvitaminB12,resp ectively.Albeititseemsthatthesepumpshavelittleconne ctionwithbacterialresistance,thedeterminationofthes tructureofMsbAto［8］ andBtuCDtodeepensourunderstandingonmultidrugtrans portmechanism. Secondarytransportsystem Onthebasisofsizeandprimaryenergyaswellassecondaryst ructure,thesystemisdividedintofourfamilies:themajor facilitatorsuperfamily,thesmallmultidrugfamily,ther esistancenodulationcelldivisionfamily,andthemul tidrugandtoxiccompoundextrusionfamily. Majorfacilitatorsuperfamily Sofar,morethantwentyMFSfamilieshavebeenrecognisedac cordingtothedegreesofsequencesimilarity.Theclinic allyimportantmultidrugtransportersareinthefamily2an d3,whichpossess14and12TMSs,respectively.Theyarealso referredtoastheDHA14andDHA12familiesduetotheability ofcatalysingdrug:Hantiport.Multiplesequencealignmen tsuggestedthatNterminalregionisrelatedtoprotontra nslocationproducingenergyfortransportsincethehighsi milarityamongthemoftheproteins;whileCterminalhalv esmaycontributetosubstraterecognitionandbindingbeca useofthelesssimilarityamongdifferentproteins.Additi onally,itisnoticeablethatthemajorityofthebacteriald rugexportersbelongtoMFS. （作者：3COME 未知本文来源于爬虫自动抓取，如有侵犯权 益请联系 service@立即删除） 。