Structural and Mechanistic Insights Into the Sulfur Transfer Protein SufU From Staphylococcus aureusPhy

Authors

• Emily Sabo, Colorado School of Mines
• Connor Nelson, Colorado School of Mines
• Delanie Huntoon, Marquette University
• Jing Yang, University of New Mexico - Albuquerque
• Martin Kirk, University of New Mexico - Albuquerque
• Simon J. George, SETI Institute
• Brian Bennett, Marquette UniversityFollow
• Jeffrey M. Boyd, Rutgers University - New Brunswick/Piscataway
• Richard C. Holz, Marquette UniversityFollow

Document Type

Article

Publication Date

12-2025

Publisher

Elsevier

Source Publication

Journal of Inorganic Biochemistry

Source ISSN

0162-0134

Abstract

Substitution of the active site Zn²⁺ ion in the sulfur transfer protein (SufU) from Staphylococcus aureus (SaSufU) with a catalytically active Co²⁺ ion revealed a S⁻➔Co²⁺ ligand-to-metal-charge-transfer (LMCT) band at 340 nm with an ε of ∼2,760M^-1 cm^-1, as well as d-d (i.e. ligand field) absorption bands at 584 nm (ε = 540 M^-1 cm^-1 ), 636 nm (ε = 580 M^-1 cm^-1) and 735 nm (ε = 220 M^-1 cm^-1). These data suggest a distorted four- or five-coordinate Co²⁺ center ligated by 3 Cys residues with a dissociation constant (K_d) of ∼600 nM. Co K-edge absorption spectra (XAS) of Co²⁺-SaSufU indicated five-coordinate Co²⁺, while extended X-ray absorption fine structure (EXAFS) spectra of Co²⁺-SaSufU revealed 2 N/O and 3 S ligands. EXAFS data for Zn²⁺-SaSufU revealed 1 N/O and 3 S ligands consistent with the proposed Cys₃Asp coordinating residues. The fifth ligand in the Co²⁺-SaSufU enzyme is either a bidentate the active site Asp ligand or an exogenous water. Upon the addition of SaSufS to either Zn²⁺-SaSufU or Co²⁺-SaSufU, XAS and EXAFS data suggest that one of the S ligands is displaced by an N/O atom donor. Interestingly, electronic absorption data suggest that this only occurs in the presence of Cys. EPR analysis of Co²⁺-SaSufU revealed temperature- and B₁-dependent transitions within both the M_s=±½ and M_s=±3/2 doublets of the S=3/2 spin system that suggested either heterogeneity of the electronic structure or an unusually small zero-field splitting for Co(II). Taken together, these data provide in-solution evidence for the mechanism of S²⁻ transfer from SaSufS to SaSufU.

Comments

Accepted version. Journal of Inorganic Biochemistry, Vol. 227 (2025): 113205. DOI. © 2025 Elsevier. Used with permission.

Recommended Citation

Sabo, Emily; Nelson, Connor; Huntoon, Delanie; Yang, Jing; Kirk, Martin; George, Simon J.; Bennett, Brian; Boyd, Jeffrey M.; and Holz, Richard C., "Structural and Mechanistic Insights Into the Sulfur Transfer Protein SufU From Staphylococcus aureusPhy" (2025). Physics Faculty Research and Publications. 188.
https://epublications.marquette.edu/physics_fac/188