Download MendeleyA novel catalytic heme cofactor in SfmD with a single thioether bond and a bis -His ligand set revealed by a de novo crystal structural and spectroscopic study.
Shin, I., Davis, I., Nieves-Merced, K., Wang, Y., McHardy, S., Liu, A.(2021) Chem Sci 12: 3984-3998
- PubMed: 34163669
- DOI: https://doi.org/10.1039/d0sc06369j
- Primary Citation of Related Structures:
6VDP, 6VDQ, 6VDZ, 6VE0 - PubMed Abstract:
SfmD is a heme-dependent enzyme in the biosynthetic pathway of saframycin A. Here, we present a 1.78 Å resolution de novo crystal structure of SfmD, which unveils a novel heme cofactor attached to the protein with an unusual H x n H xxx C motif ( n ∼ 38). This heme cofactor is unique in two respects. It contains a single thioether bond in a cysteine-vinyl link with Cys317, and the ferric heme has two axial protein ligands, i.e. , His274 and His313. We demonstrated that SfmD heme is catalytically active and can utilize dioxygen and ascorbate for a single-oxygen insertion into 3-methyl-l-tyrosine. Catalytic assays using ascorbate derivatives revealed the functional groups of ascorbate essential to its function as a cosubstrate. Abolishing the thioether linkage through mutation of Cys317 resulted in catalytically inactive SfmD variants. EPR and optical data revealed that the heme center undergoes a substantial conformational change with one axial histidine ligand dissociating from the iron ion in response to substrate 3-methyl-l-tyrosine binding or chemical reduction by a reducing agent, such as the cosubstrate ascorbate. The labile axial ligand was identified as His274 through redox-linked structural determinations. Together, identifying an unusual heme cofactor with a previously unknown heme-binding motif for a monooxygenase activity and the structural similarity of SfmD to the members of the heme-based tryptophan dioxygenase superfamily will broaden understanding of heme chemistry.
Organizational Affiliation:
Department of Chemistry, The University of Texas at San Antonio One UTSA Circle Texas 78249 USA Feradical@utsa.edu.
