Title

An EPR and VTVH MCD spectroscopic investigation of the nitrogenase assembly protein NifB

Document Type

Article

Publication Date

6-1-2021

Abstract

NifB, a radical SAM enzyme, catalyzes the biosynthesis of the L cluster (FeSC), a structural homolog and precursor to the nitrogenase active-site M cluster ([MoFeSC·R-homocitrate]). Sequence analysis shows that NifB contains the CxxCxxxC motif that is typically associated with the radical SAM cluster ([FeS]) involved in the binding of S-adenosylmethionine (SAM). In addition, NifB houses two transient [FeS] clusters (K cluster) that can be fused into an 8Fe L cluster concomitant with the incorporation of an interstitial carbide ion, which is achieved through radical SAM chemistry initiated at the [FeS] cluster upon its interaction with SAM. Here, we report a VTVH MCD/EPR spectroscopic study of the L cluster biosynthesis on NifB, which focuses on the initial interaction of SAM with [FeS] in a variant NifB protein (MaNifB) containing only the [FeS] cluster and no K cluster. Titration of MaNifB with SAM reveals that [FeS] exists in two forms, labeled [Formula: see text] and [Formula: see text]. It is proposed that these forms are involved in the synthesis of the L cluster. Of the two cluster types, only [Formula: see text] initially interacts with SAM, resulting in the generation of Z, an S = ½ paramagnetic [FeS]/SAM complex.

Publication Source (Journal or Book title)

Journal of biological inorganic chemistry : JBIC : a publication of the Society of Biological Inorganic Chemistry

First Page

403

Last Page

410

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