8C76 image
Entry Detail
PDB ID:
8C76
Title:
Light-state 2.5 Angstrom wild-type X-ray crystal structure of the cobalamin binding domain belonging to a light-dependent transcription regulator TtCarH obtained under aerobic conditions from a form 2 crystal illuminated during 5 s
Biological Source:
Source Organism:
Host Organism:
PDB Version:
Deposition Date:
2023-01-12
Release Date:
2023-08-09
Method Details:
Experimental Method:
Resolution:
2.50 Å
R-Value Free:
0.23
R-Value Work:
0.18
R-Value Observed:
0.18
Space Group:
P 21 21 21
Macromolecular Entities
Polymer Type:polypeptide(L)
Description:Probable transcriptional regulator
Chain IDs:A, B, C, D
Chain Length:215
Number of Molecules:4
Biological Source:Thermus thermophilus
Ligand Molecules
Primary Citation
Redox driven B 12 -ligand switch drives CarH photoresponse.
Nat Commun 14 5082 5082 (2023)
PMID: 37604813 DOI: 10.1038/s41467-023-40817-6

Abstact

CarH is a coenzyme B12-dependent photoreceptor involved in regulating carotenoid biosynthesis. How light-triggered cleavage of the B12 Co-C bond culminates in CarH tetramer dissociation to initiate transcription remains unclear. Here, a series of crystal structures of the CarH B12-binding domain after illumination suggest formation of unforeseen intermediate states prior to tetramer dissociation. Unexpectedly, in the absence of oxygen, Co-C bond cleavage is followed by reorientation of the corrin ring and a switch from a lower to upper histidine-Co ligation, corresponding to a pentacoordinate state. Under aerobic conditions, rapid flash-cooling of crystals prior to deterioration upon illumination confirm a similar B12-ligand switch occurs. Removal of the upper His-ligating residue prevents monomer formation upon illumination. Combined with detailed solution spectroscopy and computational studies, these data demonstrate the CarH photoresponse integrates B12 photo- and redox-chemistry to drive large-scale conformational changes through stepwise Co-ligation changes.

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