Structures of the transcriptional regulator BgaR, a lactose sensor

Abstract

The structure of BgaR, a transcriptional regulator of the lactose operon in Clostridium perfringens, has been solved by SAD phasing using a mercury derivative. BgaR is an exquisite sensor of lactose, with a binding affinity in the low-micromolar range. This sensor and regulator has been captured bound to lactose and to lactulose as well as in a nominal apo form, and was compared with AraC, another saccharide-binding transcriptional regulator. It is shown that the saccharides bind in the N-terminal region of a jelly-roll fold, but that part of the saccharide is exposed to bulk solvent. This differs from the classical AraC saccharide-binding site, which is mostly sequestered from the bulk solvent. The structures of BgaR bound to lactose and to lactulose highlight how specific and nonspecific interactions lead to a higher binding affinity of BgaR for lactose compared with lactulose. Moreover, solving multiple structures of BgaR in different space groups, both bound to saccharides and unbound, verified that the dimer interface along a C-terminal helix is similar to the dimer interface observed in AraC.

Crystal structures of human ENPP1 in apo and bound forms

“…Intact mass determination of kifunensine-treated, affinitypurified hENPP1-HIS samples was achieved by LC-MS as described previously (Newman et al, 2019). N-linked glycoprofiling was achieved by hydrophilic liquid chromatography with fluorescence and mass-spectrometry readouts (HILIC-FL-MS).…”

HilD, HilC, and RtsA Form Homodimers and Heterodimers To Regulate Expression of the Salmonella Pathogenicity Island I Type III Secretion System

“…Unlike the well-conserved C-terminal DNA binding domain, the N-terminal domains of AraC proteins, usually encoding dimerization and/or ligand binding sites (33,38), do not share much similarity at the amino acid level. However, careful analyses of predicted secondary structures of the N-terminal domains of AraC proteins and crystal structures of AraC (39), ToxT (44), ExsA (53), and BgaR from Clostridium perfringens (55) have revealed a conserved structure. Importantly, these proteins contain a hydrophobic ␣-helix at the end of the N-terminal domain that has been shown to be critical for dimer formation in AraC (39, 56), ToxT (44, 57), XylS of Pseudomonas putida (58), and ExsA (51).…”

Improvement of Pseudoalteromonas haloplanktis TAC125 as a Cell Factory: IPTG-Inducible Plasmid Construction and Strain Engineering

“…The only AraC-type transcriptional regulator of a β-galactosidase gene that has been characterized at the molecular level is BgaR of the gram positive Clostridium perfringens [ 56 , 57 , 58 ], which has been demonstrated to be regulated by lactose and partially lactulose, but not by IPTG. On the other hand, we have clearly demonstrated that pP79 induction is mainly mediated by IPTG.…”