Cobalamin decyanation by the membrane transporter BtuM.
Structure
; 32(8): 1165-1173.e3, 2024 Aug 08.
Article
em En
| MEDLINE
| ID: mdl-38733996
ABSTRACT
BtuM is a bacterial cobalamin transporter that binds the transported substrate in the base-off state, with a cysteine residue providing the α-axial coordination of the central cobalt ion via a sulfur-cobalt bond. Binding leads to decyanation of cobalamin variants with a cyano group as the ß-axial ligand. Here, we report the crystal structures of untagged BtuM bound to two variants of cobalamin, hydroxycobalamin and cyanocobalamin, and unveil the native residue responsible for the ß-axial coordination, His28. This coordination had previously been obscured by non-native histidines of His-tagged BtuM. A model in which BtuM initially binds cobinamide reversibly with low affinity (KD = 4.0 µM), followed by the formation of a covalent bond (rate constant of 0.163 s-1), fits the kinetics data of substrate binding and decyanation of the cobalamin precursor cobinamide by BtuM. The covalent binding mode suggests a mechanism not used by any other transport protein.
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Base de dados:
MEDLINE
Assunto principal:
Ligação Proteica
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Proteínas de Bactérias
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Vitamina B 12
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Modelos Moleculares
Idioma:
En
Ano de publicação:
2024
Tipo de documento:
Article