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Two Distinct Thermodynamic Gradients for Cellular Metalation of Vitamin B12

Young, Tessa R.; Deery, Evelyne; Foster, Andrew W.; Martini, Maria Alessandra; Osman, Deenah; Warren, Martin J.; Robinson, Nigel J.

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Authors

Evelyne Deery

Andrew W. Foster

Maria Alessandra Martini

Deenah Osman

Martin J. Warren



Abstract

The acquisition of CoII by the corrin component of vitamin B12 follows one of two distinct pathways, referred to as early or late CoII insertion. The late insertion pathway exploits a CoII metallochaperone (CobW) from the COG0523 family of G3E GTPases, while the early insertion pathway does not. This provides an opportunity to contrast the thermodynamics of metalation in a metallochaperone-requiring and a metallochaperone-independent pathway. In the metallochaperone-independent route, sirohydrochlorin (SHC) associates with the CbiK chelatase to form CoII-SHC. CoII-buffered enzymatic assays indicate that SHC binding enhances the thermodynamic gradient for CoII transfer from the cytosol to CbiK. In the metallochaperone-dependent pathway, hydrogenobyrinic acid a,c-diamide (HBAD) associates with the CobNST chelatase to form CoII-HBAD. Here, CoII-buffered enzymatic assays indicate that CoII transfer from the cytosol to HBAD-CobNST must somehow traverse a highly unfavorable thermodynamic gradient for CoII binding. Notably, there is a favorable gradient for CoII transfer from the cytosol to the MgIIGTP-CobW metallochaperone, but further transfer of CoII from the GTP-bound metallochaperone to the HBAD-CobNST chelatase complex is thermodynamically unfavorable. However, after nucleotide hydrolysis, CoII transfer from the chaperone to the chelatase complex is calculated to become favorable. These data reveal that the CobW metallochaperone can overcome an unfavorable thermodynamic gradient for CoII transfer from the cytosol to the chelatase by coupling this process to GTP hydrolysis.

Journal Article Type Article
Acceptance Date Apr 25, 2023
Online Publication Date May 10, 2023
Publication Date May 22, 2023
Deposit Date May 16, 2023
Publicly Available Date May 16, 2023
Journal JACS Au
Print ISSN 2691-3704
Electronic ISSN 2691-3704
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 3
Issue 5
Pages 1264-1534
DOI https://doi.org/10.1021/jacsau.3c00119
Public URL https://durham-repository.worktribe.com/output/1174237

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