Function
Highly reducing polyketide synthase; part of the gene cluster that mediates the biosynthesis of calbistrin A and related compounds. Calbistrin A is a secondary metabolite with an interesting structure that was recently found to have bioactivity against leukemia cells. It consists of two polyketides linked by an ester bond: a bicyclic decalin containing polyketide and a linear 12 carbon dioic acid structure (PubMed:30598828). The polyketide synthase calA is probably responsible for forming the decalin moiety. Because calA lacks a designated enoylreductase (ER) domain, the required activity is provided by the trans-enoyl reductase calK (PubMed:30598828). Following release from the PKS, calF then probably catalyzes the oxidation and the subsequent Diels Alder cycloisomerization that lead to the formation of the decalin moity (Probable). The decalin polyketide backbone includes two C-methyl groups, at C7 and C11 in backbone, of which the C7 position is probably methylated by the methyltransferase domain of calA. A candidate for adding the methyl group at C11, if not done by CalA, is the cluster methyltransferase calH (Probable). Several additional tailoring enzymes within the cluster could be involved in the modification of the decalin polyketide product. Those include the 3 cytochrome P450 monooxygenases CalE, CalG and CalL, of which one might be responsible for the introduction of the extra hydroxyl group attached to the backbone of the decalin moiety, at position C9 in the backbone, that allows for attachment of the linear moiety (Probable). One tailoring enzyme activity that is expected to be involved in biosynthesis of calbistrin is an acyltransferase for connecting the two polyketide synthase products, and which could be performed by the cluster acyltransferase calJ (Probable). The enzyme responsible for the biosynthesis of the linear moity, probably a second PKS, has not been identified yet (Probable).
Sequence
MAEDMPINEPLAIVGSACRFAGGVSSPSKLWDLLSNPRDVRSEILKSRFNAENYYHPDSAYHGHSNIQHSYLLEEDVAAFDSQFFGIKPVEAKAIDPQQRLLMETVYEGLESAGLTIDSLRDSDTAVYVGLMCGDYEASLLRDLSTAPVYAATGIGRSILSNRVSYFFNWHGPSMTIDTACSSSLVAVHLAAQALRSGESRVALACGSNLLLGPENYIMESKLKMLSPDGRSKMWDKDANGYARGDGVAACVLKTLSAAIEDGDDIECIIRETGVNQDGATTGITMPSATAQQALIRSTYKKAGLDLSKVNDRPQFFEAHGTGTPAGDPIEAEAISKAFFDEQYGTMVAAEPLYVGSIKTILGHTEGTAGLAALLKASLALQHSVVPPNMLLNNLSDKVAPFTKNLEILKAPKAWPSVEAGQPRRASVNSFGFGGTNAHAILESYEPRRHLQNGVTNSEAIVQFTPFVFSALSHQSLRATLSAYADHIQSNPAVNLRDMAYTLQERRSAFPYRVSFAALSADELATKIRAEVEGTKAEELGVRVSAPQTDGKRRKVLGVFTGQGAQYARMGAELLETSATARKIIQELQTCLEQLPEDLRPDFSLEEELRAAADSSRVLTGAFSFLSTVVQLLLVDLLKLAGVQFDAIVAHSSGEMAAAYAAGRLSARDAMCVAYFRGRFASKMESPNGADKKGAMLAAGMSEEDAATLCADEIFAGRVCVAAVNSSSSVTISGDEDAIDEFKLILDDENKFNRKLRVDRAYHSNHVSRRLADYVTLIQSAGVQALEPGKDAPLWISSVYGREVTTDMNLDDEYWGASVARSVQFYQALKLVLEADDYQVALEVGPHPALKGPASQTIQELGKSIPYYGVLSRGTDATVSLASSLGSLWCHLGGEQLDLTGFEKEVNDNKSSLRVVKGLPRYQWNHEASYWHESRASKKHKAQTQPFNQLLGTMMPDSAAHHLSWGHLLRASEIEWASGHQVQSQTVFPAAGYICTAFEGARVLAANRDVRLFELKDFVIHQALTFSHDDAGIEVQASIADIQRPSNDRIKAKFTYSASLGGEDLDLVAEAELHIVFGPSSERTLPHRAARPPHMISVDNERFYTFLATLGYGFEGPFKSLHTLRRKLGSSVCAVNSVPRENTFGRPLLVHPAELDGGIQSLILAYSYPDDDQLLNMHLPTSMSSIRVNPALCQSMTDISVDSRLGRNKSAGFSGDVSLYTSNSECAAIQMQGVELKPLGALTAKDDRKVFSKYQWVKNRLDGDLAACDTTVTKHHQDVLEGLERISTYYLNKLDAEVPVDSPLRKEGPHSNYLNYAHHIVELIQKGEHKVAKKEWLSDSPEDLHQATAHLSDLIDYRMMHLVGQQMPRVLRGETNMLEEMRVSNILDDYYKGAFGSREAGLWIGKIISQLAERYPHLNILEVGAGTGGATTRVLQGLSNKFLSYTFTDVSSGFFEGAAEMFSEHKDRMVFKTFDCGQDPVTQGYAEGTCDVVVAFLVIHATPDLELTMRNIRKLLKPGGLLVVGEGTNNGQPYGSAGFIFGSLPGWWLGADTGRPLSPFVSYSEWERLLKASAFSGIDSTAPQAFQDILGMTVFAAQAVDDRVNFLREPLNPDVLSQSSAAIEYPIKNLVVVGGSTERTRPLVASVTDTLKNHSAQVHTFETLSAVDFSLVDEDATVVSLSELDKPVFQDLTPDEWMAFKTLFSCPTRLFWVTSGRLSEEPFSNMTVGFARTAVFETPALRFQNVDISNLETLTPQDLAEKVLRFHASTSPVPADLKQFAWPLEPEIVIDAQGEELVPRLRHIAERNDRYNSARRPITNETDITKTPATLHNDREGWKLKELPGCASPAEHPGDRLSLEVTHSVLSALRTPYGHQFLVFGIERQSQTRFMALVPTLISVVDVSKGSAIPLPTSTLADSELLTSLAATLVSMAVVDPLMEGDTLVVQNATELFASTIATLATSKKIRIVFVADFARPNVPESWVKLEPYVTQSEIAEILPANTACFVDLSIEASENASVIPSSLPLHHRKENVSTLYSPLGWESGSSSAGTALGQLLHRAWFYAQQEAFAHRQNNATSQVVGITDLLEGLNPGNPATVIDWTLSKTHPVHVSRLDSVVFFKGDKTYWLCGLSGALGVSLVDWMIERGAKYLVLTSRNPNISPDWIAGHKRNGVTVTIVPCDVTNEPAIRAAHQFICETLPPIVGVLNGAMVLRDVSIRNMSYELMSDVFRPKVHGSIHLDRIFRDEPLDFFILFSSINCVIGNLGQANYAAANTFMCSLAAQRRKRGLAATALNVGAIIGAGYMERESSKALDLTVSKMALMHLSEQDYHQLFAEGIDSGRPGSGDEAELTTGLLDIPAATDTENTPKWHSNPAFLDFIVHQVEKNGADSGNEVVASVQDQLAACQSRSEVLAVVKGRFAMQLRNVLQMTTADEDLMALRSRDIGLDSLISVDIRSWFLKNFEVSVPVLKIMGNDTMAELAELAAEQAPASLLPGLGGEAPAPTEEAQANNAASQPVPLTVVPQSDETGSSSADSNHDGSPGESRGGSTGYTTPTTPDPHSTKGPIRIDWDAEIALPNAANIAIEIVPVARPQKIVLTGVSGLLGRSLLLRLLEDASVKKIFCIAVRRLEERLQSEELLLDDRVQYFSGNLEQPRLGLSEEDAIAIFSQADAVIHNGADTSHLKFYPEIKAANAGSTKELISLCMARKVPIHYISTVGVALFGNYESFPQVSIAAHHPPIDGSHGYVAAKWVSERLLEELQRQHGVNVWIHRPSTIVREGADNENAAAQTDWMNALMAYMRKMQAVPVMKNLRGALDFVYVKNAADSILTAVLENKPVGASYTHQVGDIVIPLDNLKEFIEDTGALNVEELPIEKWSARAVTVGLNRGVAALIDSMDDPGQPHYPRLLRQ