The following text describes a protein:
Function:
Highly reducing polyketide synthase; part of the gene cluster that mediates the biosynthesis of the phytotoxin stemphyloxin II. The first step of the pathway is the synthesis of dehydroprobetaenone I by the polyketide synthase sthA and the enoyl reductase sthE via condensation of one acetyl-CoA starter unit with 7 malonyl-CoA units and 5 methylations. The C-terminal reductase (R) domain of sthA catalyzes the reductive release of the polyketide chain. Because sthA lacks a designated enoylreductase (ER) domain, the required activity is provided the enoyl reductase sthE. The short-chain dehydrogenase/reductase sthC then catalyzes reduction of dehydroprobetaenone I to probetaenone I. The cytochrome P450 monooxygenase sthF catalyzes successive epoxidation, oxidation (resulting from epoxide opening) and hydroxylation to install a tertiary alcohol in the decaline ring to yield betaenone C from dehydroprobetaenone I and betaenone B from probetaenone I. The FAD-linked oxidoreductase sthB is responsible for the conversion of betaenone C to betaenone A via an intramolecular aldol reaction between C-1 and C-17 to form the bridged tricyclic system in betaenone A. Finally, the cytochrome P450 monooxygenase sthD catalyzes the hydroxylation of C-15 to afford the final metabolite stemphyloxin II.
Domain:
Multidomain protein; including a ketosynthase (KS) that catalyzes repeated decarboxylative condensation to elongate the polyketide backbone; a malonyl-CoA:ACP transacylase (MAT) that selects and transfers the extender unit malonyl-CoA; a dehydratase (DH) domain that reduces hydroxyl groups to enoyl groups; a methyltransferase (CMeT) domain responsible for the incorporation of methyl groups; a ketoreductase (KR) domain that catalyzes beta-ketoreduction steps; an acyl-carrier protein (ACP) that serves as the tether of the growing and completed polyketide via its phosphopantetheinyl arm; and a C-terminal reductase (R) domain that catalyzes the reductive release of the polyketide chain.
Sequence:
MSHNKPVNEPIVIIGSGCRFAGGANSPSKLWDLLRNPKDLRSDVTSRFNSQGYYHKDGTHHGHMNVLQSYLIGEDTRLFDAEFFGVNPVEAKAMDPQQRLLLEVVYEAIESAGLSMERMRGSDTAVFAGLMCGDYEAMMLRDLDQAPTHFAIGTSRAILSNRVSYFFDWHGPSITIDTACSSSLVAVHHAVQALRSGDSHAAIACGSNLILGPEMYVIESKLKMLSPDGLSRMWDKDANGYARGEGVTAVVLKTLSQALADNDRIEAVIRETGVNQDGATPGITMPSASAQRALIHSVYRKAGLDPESPNDRPQYIESHGTGTPAGGSIKTVLGHTEGSAGIAALLKVTKAIQNATVPPNLWFQQLNHKLEPFYGNIQIPTQPVTWPATEKRRRKRASINNFGFGGTNAHAIVEGYEPKEEIPPPSFHHVDATVSTPFVFSAASKESLRANLAAYALHLDAHPQISTRDLAYTLRERRSVLPFRIAFPESNTKDLKLSIAARLSESDGEGLGVRTWAANNGGSSKLLGIFTGQGAQYARMGTELLAQTNMARKTLEELEGYLAELPEEDRPSWSLQSELLADPSVSRVGEAAISQPLCTAVQIILVKLLCSAKVRFDTVIGHSSGEIAAAYAAGYLSARDALLVAYYRGLHCKLAASPNGNVKGAMLAAGTSLEDATELCEDEEFSGRINVAASNSSSSVTISGDEDAIDELATVFDDEKKFNRRLKVDTAYHSKHMLPCFEPYVASLRRVGITVLPGNDQCTWISSVHEGRAINPATDELADVYWAQNMTKPVLFSQAVQAAVAPVRGGEPFAAALEVGPHAALAGPAKQTIQEVAQKEIPYHGSLVRGENATKAFATCLGFLWERLDAASLDLGSCEAALSSSGGVQQYTVLADLPTYQWKHETVYWAESRRSRRMRLREGPFHQLLGNVSPDSAPHILRWKNVLKPKEMTWLEGHQVQNQVVLPAATYICTAIEAARSLAQGKNIQLIELSNFCIHNAITFDQNDVGVEVLVELSRINVKENHVNATFTYTAGLGDETNDLALAANGELNILLVDDDPSLALFPERQEPPPHMIPVQPSRLYDFMKGLEYDFSGPFQSLAKLERKLGTATCLAKKARKSVPDADDLLVHPVDLDAAFQSVMLAYSYPGDDQLRLLHLPTSIERLRVNPAALSSQKYVENDTTILDSTCTTADRAEPGNGFSGSVNMYAAGFDHAAIQVEQVKFKPVGSDAKDDRNVFYKMHWVPSKPDGLLAAASVPITERDRKLMFVLSRIAAYYLRKFDEMIAEDDPARLESPLCHYMRYARHMMGLLRAGEHKWAYKEWLQDTEQDVFDDIASKGFQDNSDVRIMLLVGSTMPRVFRRETTMLEHFRTSGLLDEYYSNGFGTKQCTLWVAGVLKQLADCNPHLNLLEIGAGTGSATKTILKSVGHDFASYTFTDISSSFFENAAETFSDYGSRMVFKVCNAENDPVEQGFEAGTYDVVIAFMVIHACAKLDEAVANLRKLLKPGGLLVLGEGASDGAMQAGAGFIFGTLPGWWRGVDEGRTLSPLVSASEWQVILRDAGFSGIDTMSPPELFDAFGITLFVSTAVDERIEFVRNPRAKASRAVYNKVVVIGGITSTIAKLAEEIQTVLTPLAIQVLLCTSLEDLQENVLDDETVIISLVDLEAPVFKDITSERWYKFRLLFETKREILWLTSGRLEDEPYSNMTVGFGRSAMHEEETLRVQYLDVADVSQLNAVMVMQYLLRFTSSELDKSDILYTKEPEVIIDANGRELVPRLFTIQAANNRLNSVTRPIYEDVDTSQSVVELRYAKEEPSFRKLSRYEVSAKLEPSHDTTIKLRVAYSVISALRCPAGYQYLIMGFDESGARRVALVNSLTSVLCVPLKSTILCELYDMSEPSYLTLLAAEIIAMTIVDPLFTGQKLAILNASKLIIQAIASYATAKGVETTFIVDAGGEFVPKDVAVQSHLPLYPSRSDMSFILPTNLACFVSFSALNKADSEDAMKSLLPFYCQKMNTSTLFSTHGVDTGALGATAQHVLSRAISSRKGRVIDWTPPSTSLSVRITRFEMTQLFKADKTYWLVGLSGALGISLCDWMIERGVKYLVLTSRNPKIDERWIENHEKHGVMIKILLCDVTDEAAIKDVHQTIVRTLPPIAGLLNGAMVLRDVSVRNMEYAQVTDVIRPKVLGSIHLDRIFHDIDLDFFVLLSSINCVIGNVGQANYAAANMGMIGVAGHRRKRGLRSSVVNVGAIIGVGYITQSDRQLDVTVAKTAMMHLSEQDFHQIFAECMEAGHLDNDSGPEISTGLLEITPDTIDIPPWYSDPKFKRFQVHQAAAGAGKAEVANSASTQELLLACRSQADITKVVQQAYCAQLRRILQVSTADEDLMMMRGVDLGFDSLLSVDVRSWFLKNFRVSIPVLKIMANDVRMSTLVDLAAESIPAELIPHVQQQQQQAGRQDASSNTSSDDETASTLPTSPESASPGTSTPVPEKDISPVDTFNSVDWYFETTPPSISTFSELTSAPAPRSDPKVVVLTGCSGLLGHHLLSTLIAQPSIRKIICLAVRSLPSRLSSGELPLPGDKIEYHAGDLTAPQLGLSTSTWISIFKQADAVIHNGSDTSHLKYYSALKLANVDSTKQLVSTCLQRMIPFHYVSSAGVALFAERDAFPPVSCTTTGKTPPADGSHGYMCGKWVCEKMLERVYEQYHLPIVIQRPSTIIRSGEDAAVERAGFDWVNSLLHFAHQTQTVPRVDHNAGAFDLVSVDTCCSDVARKLTRATKERITYVNNVGDVVIPMASMADVGLDRIGKRYNVLTMDEWTKTVVEAGMHPAVAALIETFDEPGVEKYPMLLRE