6nkh

Structural highlights

Function

MALC_MALAU Short-chain dehydrogenase/reductase; part of the gene cluster that mediates the biosynthesis of malbrancheamide, a dichlorinated fungal indole alkaloid that belongs to a family of natural products containing a characteristic bicyclo[2.2.2]diazaoctane core (PubMed:23213353, PubMed:28777910, PubMed:31548667). The first step of malbrancheamide biosynthesis involves coupling of L-proline and L-tryptophan by malG, a bimodular NRPS, to produce L-Pro-L-Trp aldehyde through reductive offloading (PubMed:23213353, PubMed:31548667). This compound undergoes spontaneous cyclization and dehydration to give a dienamine which is reverse prenylated at C-2 by malE (PubMed:31548667). The other prenyltransferase present in the cluster, malB, displays modest activity, suggesting that may be a redundant gene in the pathway (PubMed:31548667). Subsequently, a [4+2] Diels-Alder cyclo-addition catalyzed by the bifunctional enzyme malC forms the characteristic bicyclo[2.2.2]diazaoctane ring of premalbrancheamid (PubMed:31548667). The first reaction catalyzed is a NADPH-dependent reduction reaction in which the nicotinamide cofactor is a stoichiometric reagent (PubMed:31548667). Either NADH or NADPH is effective as a cofactor (PubMed:31548667). Finally, the flavin-dependent halogenase malA catalyzes the iterative dichlorination of the indole ring of premalbrancheamide to yield C-9 monochlorinated malbrancheamide B, C-8 monochlorinated isomalbrancheamide B, and dichlorinated malbrancheamide (PubMed:28777910, PubMed:31548667). MalA is also able to brominate premalbrancheamide at C-9 to yield malbrancheamide C, and, to a lesser extend, at C-8 to yield isomalbrancheamide C (PubMed:28777910). Finally, malA can brominate C-9 monochlorinated malbrancheamide B at C-8 to yield malbrancheamide D, or C-8 monochlorinated isomalbrancheamide B at C-9 to produce isomalbrancheamide D (PubMed:28777910).^{[1] [2] [3]}

References

1. ↑ Li S, Anand K, Tran H, Yu F, Finefield JM, Sunderhaus JD, McAfoos TJ, Tsukamoto S, Williams RM, Sherman DH. Comparative analysis of the biosynthetic systems for fungal bicyclo[2.2.2]diazaoctane indole alkaloids: the (+)/(-)-notoamide, paraherquamide and malbrancheamide pathways. Medchemcomm. 2012 Aug;3(8):987-996. PMID:23213353 doi:10.1039/C2MD20029E
2. ↑ Fraley AE, Garcia-Borras M, Tripathi A, Khare D, Mercado-Marin EV, Tran H, Dan Q, Webb G, Watts K, Crews P, Sarpong R, Williams RM, Smith JL, Houk KN, Sherman DH. Function and structure of MalA/MalA', iterative halogenases for late-stage C-H functionalization of indole alkaloids. J Am Chem Soc. 2017 Aug 4. doi: 10.1021/jacs.7b06773. PMID:28777910 doi:http://dx.doi.org/10.1021/jacs.7b06773
3. ↑ Dan Q, Newmister SA, Klas KR, Fraley AE, McAfoos TJ, Somoza AD, Sunderhaus JD, Ye Y, Shende VV, Yu F, Sanders JN, Brown WC, Zhao L, Paton RS, Houk KN, Smith JL, Sherman DH, Williams RM. Fungal indole alkaloid biogenesis through evolution of a bifunctional reductase/Diels-Alderase. Nat Chem. 2019 Sep 23. pii: 10.1038/s41557-019-0326-6. doi:, 10.1038/s41557-019-0326-6. PMID:31548667 doi:http://dx.doi.org/10.1038/s41557-019-0326-6