Digital Repository

Optimized Substrate Positioning Enables Switches in the C–H Cleavage Site and Reaction Outcome in the Hydroxylation–Epoxidation Sequence Catalyzed by Hyoscyamine 6β-Hydroxylase

Show simple item record

dc.contributor.author Wenger, Eliott S. en_US
dc.contributor.author SIL, DEBANGSU et al. en_US
dc.date.accessioned 2024-09-06T10:42:11Z
dc.date.available 2024-09-06T10:42:11Z
dc.date.issued 2024-08 en_US
dc.identifier.citation Journal of the American Chemical Society, 146(35), 24271–24287. en_US
dc.identifier.issn 0002-7863 en_US
dc.identifier.issn 1520-5126 en_US
dc.identifier.uri https://doi.org/10.1021/jacs.4c04406 en_US
dc.identifier.uri http://dr.iiserpune.ac.in:8080/xmlui/handle/123456789/9074
dc.description.abstract Hyoscyamine 6β-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─analogously to mechanisms proposed for the Fe/2OG halogenases and, in our more recent study, N-acetylnorloline synthase (LolO)─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 6β-hydroxyhyoscyamine suggest that a modest (∼10°) 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 2H2O, 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. en_US
dc.language.iso en en_US
dc.publisher American Chemical Society en_US
dc.subject Ketoglutarate Dioxygenase en_US
dc.subject Taudspin Fe(Iv) en_US
dc.subject Complexaliphatic en_US
dc.subject Halogenaseclavaminate en_US
dc.subject Synthase en_US
dc.subject Crystal-Structure en_US
dc.subject Ironintermediate en_US
dc.subject Mechanis en_US
dc.subject Menzyme en_US
dc.subject Activation en_US
dc.subject 2024 en_US
dc.subject 2024-SEP-WEEK1 en_US
dc.subject TOC-SEP-2024 en_US
dc.title Optimized Substrate Positioning Enables Switches in the C–H Cleavage Site and Reaction Outcome in the Hydroxylation–Epoxidation Sequence Catalyzed by Hyoscyamine 6β-Hydroxylase en_US
dc.type Article en_US
dc.contributor.department Dept. of Chemistry en_US
dc.identifier.sourcetitle Journal of the American Chemical Society, en_US
dc.publication.originofpublisher Foreign en_US


Files in this item

Files Size Format View

There are no files associated with this item.

This item appears in the following Collection(s)

Show simple item record

Search Repository


Advanced Search

Browse

My Account