Structural study of TcaR and its complexes with multiple antibiotics from Staphylococcus epidermidis

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• TcaR and IcaR negatively regulate the ica locus, controlling poly-N-acetylglucosamine production and biofilm formation in Staphylococcus epidermidis.
• The precise DNA binding region and regulatory mechanism of TcaR remained unclear despite its interaction with the ica promoter.

Purpose of the Study:

• To elucidate the 3D structure of TcaR in its apo and complex forms with salicylate and antibiotics.
• To determine the mechanism of TcaR-mediated transcriptional regulation and its interaction with DNA.

Main Methods:

• X-ray crystallography to determine the 3D structures of TcaR.
• DNA-binding assays to identify TcaR consensus binding sequences and affinities.
• In vivo assays to assess the impact of antimicrobial compounds on TcaR-DNA interaction and biofilm formation.

Main Results:

• The 3D structures revealed a large conformational change in TcaR's DNA-binding lobe upon complex formation.
• A consensus binding sequence of two [approximately TTNNAA] hexamers within a 16 bp sequence was deduced for TcaR dimers.
• Six TcaR dimers bind to specific DNA segments, with repressor activity inhibited by salicylate and antimicrobial compounds, which also induced biofilm formation in vivo.

Conclusions:

• Antibiotic binding to TcaR induces conformational changes, altering its DNA-binding activity and transcriptional repression.
• Antimicrobial compounds can inhibit TcaR-DNA interaction, paradoxically promoting biofilm formation in Staphylococcus epidermidis.
• These findings provide insights into how antibiotic exposure influences bacterial antibiotic resistance via biofilm formation.