Crystal structure of Bacillus subtilis GabR, an autorepressor and transcriptional activator of gabT

Raji Edayathumangalam, Rui Wu, Roman Garcia, Yuguang Wang, Wei Wang, Cheryl A. Kreinbring, Alicia Bach, Jingling Liao, Todd A. Stone, Thomas C. Terwilliger, Quyen Q. Hoang, Boris R. Belitsky, Gregory A. Petsko, Dagmar Ringe, Dali Liu

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41 Scopus citations

Abstract

Bacillus subtilis GabR is a transcription factor that regulates gamma-aminobutyric acid (GABA) metabolism. GabR is a member of the understudied MocR/GabR subfamily of the GntR family of transcription regulators. A typical MocR/GabR-Type regulator is a chimeric protein containing a short N-Terminal helix-Turn-helix DNA-binding domain and a long C-Terminal pyridoxal 5α-phosphate (PLP)-binding putative aminotransferase domain. In the presence of PLP and GABA, GabR activates the gabTD operon, which allows the bacterium to use GABA as nitrogen and carbon sources. GabR binds to its own promoter and represses gabR transcription in the absence of GABA. Here, we report two crystal structures of fulllength GabR from B. subtilis: a 2.7-A structure of GabR with PLP bound and the 2.55-A apo structure of GabR without PLP. The quaternary structure of GabR is a head-To-Tail domain-swap homodimer. Each monomer comprises two domains: an N-Terminal winged-helix DNA-binding domain and a C-Terminal PLP-binding type I aminotransferase-like domain. The winged-helix domain contains putative DNA-binding residues conserved in other GntR-Type regulators. Together with sedimentation velocity and fluorescence polarization assays, the crystal structure of GabR provides insights into DNA binding by GabR at the gabR and gabT promoters. The absence of GabR-mediated aminotransferase activity in the presence of GABA and PLP, and the presence of an active site configuration that is incompatible with stabilization of the GABA external aldimine suggest that a GabR aminotransferase-like activity involving GABA and PLP is not essential to its primary function as a transcription regulator.

Original languageEnglish (US)
Pages (from-to)17820-17825
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume110
Issue number44
DOIs
StatePublished - Oct 29 2013

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    Edayathumangalam, R., Wu, R., Garcia, R., Wang, Y., Wang, W., Kreinbring, C. A., Bach, A., Liao, J., Stone, T. A., Terwilliger, T. C., Hoang, Q. Q., Belitsky, B. R., Petsko, G. A., Ringe, D., & Liu, D. (2013). Crystal structure of Bacillus subtilis GabR, an autorepressor and transcriptional activator of gabT. Proceedings of the National Academy of Sciences of the United States of America, 110(44), 17820-17825. https://doi.org/10.1073/pnas.1315887110