9y6k | pdb_00009y6k

Avermitilol synthase T215V: Complex with Mg, inorganic pyrophosphate, and benzyltriethyl ammonium cation

spinqualitylabelsall models 9y6k, resolution 1.42Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structural highlights 9y6k is a 1 chain structure with sequence from Streptomyces avermitilis. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance. Method: X-ray diffraction, Resolution 1.42Å Ligands: BTM, DPO, EDO, MG Resources: FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT Function TPC1_STRAW Catalyzes the cyclization of farnesyl diphosphate to avermitilol. Publication Abstract from PubMed Avermitilol synthase from Streptomyces avermitilis (SaAS) is a high-fidelity class I terpene cyclase that converts farnesyl diphosphate into a highly strained, 6-6-3 tricyclic sesquiterpene alcohol. The mechanism of avermitilol formation proceeds through a 10-3 bicyclic intermediate, bicyclogermacrene, which undergoes proton-initiated anti-Markovnikov addition to two separate C horizontal lineC bonds in a transannulation mechanism that forms the 6-6-3 tricyclic skeleton, with quenching by water to yield avermitilol. Small amounts of a side product, viridifloral, result from Markovnikov addition to one of the reactive C horizontal lineC bonds. Here, we present enzymological studies of SaAS to establish the substrate scope and metal ion dependence for catalysis, and we present crystal structures of SaAS complexed with a variety of ligands that partially mimic carbocation intermediates in catalysis. Interestingly, these structures show that two water molecules remain trapped in a polar crevice in the active site regardless of the ligand bound. Structure-activity relationships for site-specific mutants yield key insight into the catalytic importance of these trapped water molecules. Specifically, T215 normally hydrogen bonds with water molecule W1, but the T215V substitution breaks this hydrogen bond and causes W1 to shift by 1.3 A to form a hydrogen bond with W300. Avermitilol generation is completely lost in this mutant, but the generation of viridifloral and another side product is enhanced. We conclude that the T215V substitution causes water molecule W1 to align for reaction with the tertiary and not the secondary carbon in the reactive C horizontal lineC bond of bicyclogermacrene. Structure and Mechanism of Avermitilol Synthase, a Sesquiterpene Cyclase That Generates a Highly Strained 6-6-3 Tricyclic Alcohol.,Gaynes MN, Osika KR, Christianson DW Biochemistry. 2025 Dec 16;64(24):4830-4840. doi: 10.1021/acs.biochem.5c00565. , Epub 2025 Dec 1. PMID:41326024 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

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