8cvc

Structure of Hyoscyamine 6-beta Hydroxylase in complex with vanadyl, succinate, and 6-OH-hyoscyamine

spinqualitylabelsall models 8cvc, resolution 1.79Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structural highlights 8cvc is a 1 chain structure with sequence from Atropa belladonna. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance. Method: X-ray diffraction, Resolution 1.791Å Ligands: EDO, FMT, O, OVR, SIN, SR, V Resources: FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT Function Q9XJ43_ATRBE Publication Abstract from PubMed Hyoscyamine 6beta-hydroxylase (H6H) is an iron(II)- and 2-oxoglutarate-dependent (Fe/2OG) oxygenase that produces the prolifically administered antinausea drug, scopolamine. After its namesake hydroxylation reaction, H6H then couples the newly installed C6 oxygen to C7 to produce the drug's epoxide functionality. Oxoiron(IV) (ferryl) intermediates initiate both reactions by cleaving C-H bonds, but it remains unclear how the enzyme switches the target site and promotes (C6)O-C7 coupling in preference to C7 hydroxylation in the second step. In one possible epoxidation mechanism, the C6 oxygen would horizontal line analogously to mechanisms proposed for the Fe/2OG halogenases and, in our more recent study, N-acetylnorloline synthase (LolO) horizontal line coordinate as alkoxide to the C7-H-cleaving ferryl intermediate to enable alkoxyl coupling to the ensuing C7 radical. Here, we provide structural and kinetic evidence that H6H does not employ substrate coordination or repositioning for the epoxidation step but instead exploits the distinct spatial dependencies of competitive C-H cleavage (C6 vs C7) and C-O-coupling (oxygen rebound vs cyclization) steps to promote the two-step sequence. Structural comparisons of ferryl-mimicking vanadyl complexes of wild-type H6H and a variant that preferentially 7-hydroxylates instead of epoxidizing 6beta-hydroxyhyoscyamine suggest that a modest ( approximately 10 degrees ) shift in the Fe-O-H(C7) approach angle is sufficient to change the outcome. The 7-hydroxylation:epoxidation partition ratios of both proteins increase more than 5-fold in (2)H(2)O, reflecting an epoxidation-specific requirement for cleavage of the alcohol O-H bond, which, unlike in the LolO oxacyclization, is not accomplished by iron coordination in advance of C-H cleavage. Optimized Substrate Positioning Enables Switches in the C-H Cleavage Site and Reaction Outcome in the Hydroxylation-Epoxidation Sequence Catalyzed by Hyoscyamine 6beta-Hydroxylase.,Wenger ES, Martinie RJ, Ushimaru R, Pollock CJ, Sil D, Li A, Hoang N, Palowitch GM, Graham BP, Schaperdoth I, Burke EJ, Maggiolo AO, Chang WC, Allen BD, Krebs C, Silakov A, Boal AK, Bollinger JM Jr J Am Chem Soc. 2024 Sep 4;146(35):24271-24287. doi: 10.1021/jacs.4c04406. Epub , 2024 Aug 22. PMID:39172701 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

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