5frb | pdb_00005frb
Crystal structure of sterol 14-alpha demethylase (CYP51B) from a pathogenic filamentous fungus Aspergillus fumigatus in complex with a tetrazole-based inhibitor VT-1598
Structural highlights
FunctionCP51B_ASPFU Sterol 14-alpha demethylase; part of the third module of ergosterol biosynthesis pathway that includes the late steps of the pathway (PubMed:18191972, PubMed:26459890, PubMed:29439966, PubMed:9184358). Demethylates eburicol to yield 4,4,24-trimethyl ergosta-8,14,24(28)-trienol (PubMed:18191972, PubMed:26459890, PubMed:29439966, PubMed:9184358). The third module or late pathway involves the ergosterol synthesis itself through consecutive reactions that mainly occur in the endoplasmic reticulum (ER) membrane. Firstly, the squalene synthase erg9 catalyzes the condensation of 2 farnesyl pyrophosphate moieties to form squalene, which is the precursor of all steroids. Squalene synthase is crucial for balancing the incorporation of farnesyl diphosphate (FPP) into sterol and nonsterol isoprene synthesis. Secondly, squalene is converted into lanosterol by the consecutive action of the squalene epoxidase erg1 and the lanosterol synthase erg7. Then, the delta(24)-sterol C-methyltransferase erg6 methylates lanosterol at C-24 to produce eburicol. Eburicol is the substrate of the sterol 14-alpha demethylase encoded by cyp51A and cyp51B, to yield 4,4,24-trimethyl ergosta-8,14,24(28)-trienol. The C-14 reductase erg24 then reduces the C14=C15 double bond which leads to 4,4-dimethylfecosterol. A sequence of further demethylations at C-4, involving the C-4 demethylation complex containing the C-4 methylsterol oxidases erg25A or erg25B, the sterol-4-alpha-carboxylate 3-dehydrogenase erg26 and the 3-keto-steroid reductase erg27, leads to the production of fecosterol via 4-methylfecosterol. The C-8 sterol isomerase erg2 then catalyzes the reaction which results in unsaturation at C-7 in the B ring of sterols and thus converts fecosterol to episterol. The sterol-C5-desaturase erg3B then catalyzes the introduction of a C-5 double bond in the B ring to produce 5-dehydroepisterol. The 2 other sterol-C5-desaturases, erg3A and erg3C, seem to be less important in ergosterol biosynthesis. The C-22 sterol desaturase erg5 further converts 5-dehydroepisterol into ergosta-5,7,22,24(28)-tetraen-3beta-ol by forming the C-22(23) double bond in the sterol side chain. Finally, ergosta-5,7,22,24(28)-tetraen-3beta-ol is substrate of the C-24(28) sterol reductases erg4A and erg4B to produce ergosterol. Possible alternative sterol biosynthetic pathways might exist from fecosterol to ergosterol, depending on the activities of the erg3 isoforms (PubMed:16110826, PubMed:18191972) (Probable).[1] [2] [3] [4] [5] [6] As a target of azole drugs, plays a crucial role in azole susceptibility.[7] [8] [9] [10] Publication Abstract from PubMedWithin the past decades, the incidence and complexity of human fungal infections have increased, and therefore the need for safer and more efficient, broad-spectrum antifungal agents is high. Herein, we characterize the new tetrazole-based drug candidate VT-1598 as an inhibitor of sterol 14alpha-demethylase (CYP51B) from the filamentous fungi Aspergillus fumigatus VT-1598 displayed a high binding affinity to the enzyme in solution (with the Kd of 13+/-1 nM) and in the reconstituted enzymatic reaction revealed the inhibitory potency stronger than the potencies of all other simultaneously tested antifungal drugs, including fluconazole, voriconazole, ketoconazole, and posaconazole. The X-ray structure of the VT-1598/A. fumigatus CYP51 complex has been determined depicting the distinctive binding mode of the inhibitor in the enzyme active site and suggesting the molecular basis of the improved drug potency and broad-spectrum antifungal activity. These data show the formation of an optimized hydrogen bond between the phenoxymethyl oxygen of VT-1598 and the imidazole ring nitrogen of His-374, the CYP51 residue that is highly conserved across fungal pathogens and fungi-specific. Comparative structural analysis of A. fumigatus CYP51/voriconazole and C. albicans CYP51/VT-1161 complexes supports the role of H-bonding in fungal CYP51-inhibitor complexes, and emphasizes the importance of an optimal distance between this interaction and the inhibitor-heme iron interaction. Cellular experiments using two A. fumigatus strains (32820 and 1022) displayed direct correlation between the effects of the drugs on the CYP51B activity and fungal growth inhibition, indicating the noteworthy anti-A. fumigatus potency of VT-1598 and confirming its promise as a broad-spectrum antifungal agent. Crystal structure of the new investigational drug candidate VT-1598 in complex with Aspergillus fumigatus sterol 14alpha-demethylase provides insights into its broad-spectrum antifungal activity.,Hargrove TY, Garvey EP, Hoekstra WJ, Yates CM, Wawrzak Z, Rachakonda G, Villalta F, Lepesheva GI Antimicrob Agents Chemother. 2017 May 1. pii: AAC.00570-17. doi:, 10.1128/AAC.00570-17. PMID:28461309[11] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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