X-ray crystallographic structure of a transcriptional activator of virulence factor in enterococcus faecalis, ELRR

Full text: RNPP family of transcriptional regulators is present exclusively in Gram positive bacteria and regulates factors involved in virulence, invasion, biofilm formation, etc. That family shares structure, functions and also the regulation by peptides. ElrR protein is a transcriptional regulator of Rggfamily, that positively regulates ElrA, which is a virulence factor of Enterococcus faecalis. Rgg family was proposed to belong to RNPP family. Here we present the crystallographic structure of APO ElrR obtained at 2.15Å resolution. We solved the phase problem using diffraction data at 2.55 Å resolution of Se-Met-ElrR crystals measured on the absorption edge (λ=0.979096 Å) of Selenium atoms, collected at LNLS Synchrotron, Brazil. We then improved the resolution using a dataset obtained at home (λ=1,5418 Å) which diffracted at 2.15 Å resolution. This structure was refined to Rwork 0,2024 e Rfree 0,258. Crystals presented space group P1 with crystallographic cell a 70.800 b 75.330 c 85.280 α 112.99 β 89.93 γ 103.88 which contains two homodimers. The crystallographic model has shown the same fold in ElrR as PgrX and RGG2sd structures, in spite of the low sequence identity (under 13% in all cases). The structure presents a helix-turn-helix XRE-type domain on the N-terminal, a 5-helix central domain and a C-terminal domain build of tetratricopepitides (TPR)-like repetitions. The interface between the Central and the C-terminal domains contains the alosteric site, like in distant homologous proteins of the RNPP family, but the cleft on the alosteric site in ElrR is wider. Then, ElrR ligand can be bigger than those found in these homologous structures. (author)