bi0c00347_si_001.pdf (3.43 MB)
Staphylococcus aureus Glucose-Induced Biofilm Accessory Protein A (GbaA) Is a Monothiol-Dependent Electrophile Sensor
journal contribution
posted on 2020-07-29, 18:34 authored by Abhinaba Ray, Katherine A. Edmonds, Lauren D. Palmer, Eric P. Skaar, David P. GiedrocStaphylococcus aureus is a commensal pathogen
that has evolved to protect itself from unfavorable conditions by
forming complex community structures termed biofilms. The regulation
of the formation of these structures is multifactorial and in S. aureus involves a number of transcriptional regulators.
GbaA (glucose-induced biofilm accessory protein A) is a tetracycline
repressor (TetR) family regulator that harbors two conserved Cys residues
(C55 and C104) and impacts the regulation of formation of poly-N-acetylglucosamine-based biofilms in many methicillin-resistant S. aureus (MRSA) strains. Here, we show that GbaA-regulated
transcription of a divergently transcribed operon in a MRSA strain
can be induced by potent electrophiles, N-ethylmaleimide
and methylglyoxal. Strikingly, induction of transcription in cells
requires C55 or C104, but not both. These findings are consistent
with in vitro small-angle X-ray scattering, chemical
modification, and DNA operator binding experiments, which reveal that
both reduced and intraprotomer (C55–C104) disulfide forms of
GbaA have very similar overall structures and each exhibits a high
affinity for the DNA operator, while DNA binding is strongly inhibited
by derivatization of one or the other Cys residues via formation of
a mixed disulfide with bacillithiol disulfide or a monothiol derivatization
adduct with NEM. While both Cys residues are reactive toward electrophiles,
C104 in the regulatory domain is the more reactive thiolate. These
characteristics enhance the inducer specificity of GbaA and would
preclude sensing of generalized cellular oxidative stress via disulfide
bond formation. The implications of the findings for GbaA function
in MRSA strains are discussed.