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1、DirectedMolecularEvolutionofProteins:orHowtoImproveEnzymesforBiocatalysis.EditedbySusanneBrakmannandKaiJohnssonCopyrightã2002Wiley-VCHVerlagGmbH&Co.KGaAISBNs:3-527-30423-1(Hardback);3-527-60064-7(Electronic)10ExploringtheDiversityofHemeEnzymesthroughDirectedEvolu
2、tionPatrickC.CirinoandFrancesH.Arnold10.1IntroductionEnzymesarecapableofclean,specificcatalysiswithhighturnoverrates.Theyhavealreadyprovenusefulinnumeroussyntheticapplications,particularlyforthehighvalueandoftenchiralcompoundsdemandedbythepharmaceutical,agricultu
3、ral,andfoodindustries.RedoxenzymessuchasperoxidasesandcytochromeP450mono-oxygenasescatalyzevaluablereactionsonavastspectrumofsubstrates.Despitetheirimpressivesyntheticpotential,theseenzymeshaveenjoyedonlylimiteduseduetotheirrelativecomplexity,instabilityand,insom
4、ecases,lowcatalyticefficiency.De-mandsforclean,economicaloxidationprocessesandforincreasinglycomplexandspecificoxidationproductsallpointinthedirectionofbiocatalyticroutes.Directedevolutionmaybeabletoeliminatesomeoftheshortcomingsofenzymes,whileim-provingandharnes
5、singtheirnaturalcatalyticpower.Metalloporphyrinsaresynthesizednaturallyandutilizedbiologicallyasredoxcat-alysts,andassuchareessentialtolife.Thesemetalcomplexeshavedifferentchemicalfunctions(see[1]);naturehasdiscoveredtheabilitytomodulatethefunctionbyin-corporatin
6、gthemintoproteinswhichallowforatremendousdiversityofarchitectureandchemicalenvironmentssurroundingtheprostheticgroup.Withintheproteinframeworktheprostheticgroupbecomesaversatiletoolwithvarying,highlyspecia-lizedcapabilities.Hemeservesastheactivecenterindifferentf
7、amiliesofproteinsclassifiedbystruc-turalsimilarity(e.g.heme-bindingperoxidases,cytochromesP450,globins,catalases).Withinthesefamiliesthemetalloporphyrinhasaprimaryfunction(e.g.hydroxylationoroxygenbinding),butthereisalsoconsiderablefunctionaloverlapamongthem.Thep
8、roteinregulatesthefunction,butitisnotknownwhethertheparticularfoldsthatcharacterizeeachclassarerequiredforoptimalfunctionofthatclass.Onecouldarguethatnaturehas
