Crystal structure of a gamma-butyrolactone autoregulator receptor protein in Streptomyces coelicolor A3(2)

The gamma-butyrolactone-type autoregulator/receptor systems in the Gram-positive bacterial genus Streptomyces regulate morphological differentiation or antibiotic production, or both. The autoregulator receptors act as DNA-binding proteins, and on binding their cognate ligands (gamma-butyrolactones) they are released from the DNA, thus serving as repressors. The crystal structure of CprB in Streptomyces coelicolor A3(2), a homologue of the A-factor-receptor protein, ArpA, in Streptomyces griseus, was determined. The overall structure of CprB shows that the gamma-butyrolactone receptors belong to the TetR family. CprB is composed of two domains, a DNA-binding domain and a regulatory domain. The regulatory domain contains a hydrophobic cavity, which probably serves as a ligand-binding pocket. On the basis of the crystal structure of CprB and on the analogy of the characteristics of ligand-TetR binding, the binding of gamma-butyrolactones to the regulatory domain of the receptors is supposed to induce the relocation of the DNA-binding domain through conformational changes of residues located between the ligand-binding site and the DNA-binding domain, which would result in the dissociation of the receptors from their target DNA.     

细菌GntR家族转录调控因子的研究进展

GntR家族转录调控因子是细菌中分布最为广泛的一类螺旋–转角–螺旋(helix-turn-helix,HTH)转录调控因子,此家族转录调控因子包含两个功能域,分别是N端的DNA结合结构域和C端的效应物结合结构域/寡聚化作用结构域。DNA结合结构域的氨基酸序列是非常保守的,但效应物结合结构域/寡聚化作用结构域的氨基酸序列却存在很大的差异性。目前许多GntR家族的转录调控因子已经被鉴定,这些转录因子调控细菌许多不同的细胞过程,如运动性、葡萄糖代谢、细菌的耐药性、病原细菌的致病力等。本文主要阐述了GntR家族转录调控因子的发现、二级结构、生物学功能、调控模式等方面的研究进展,旨在为研究者全面、深入地了解GntR家族转录调控因子的功能及作用机理提供帮助。     

Modulation of the sensitivity of FimB recombination to branched-chain amino acids and alanine in Escherichia coli K-12

Phase variation of type 1 fimbriae of Escherichia coli requires the site-specific recombination of a short invertible element. Inversion is catalyzed by FimB (switching in either direction) or FimE (inversion mainly from on to off) and is influenced by auxiliary factors integration host factor (IHF) and leucine-responsive regulatory protein (Lrp). These proteins bind to sites (IHF site II and Lrp sites 1 and 2) within the invertible element to stimulate recombination, presumably by bending the DNA to enhance synapses. Interaction of Lrp with a third site (site 3) cooperatively with sites 1 and 2 (termed complex 1) impedes recombination. Inversion is stimulated by the branched-chain amino acids (particularly leucine) and alanine, and according to a current model, the amino acids promote the selective loss of Lrp from site 3 (complex 2). Here we show that the central portion of the fim invertible element, situated between Lrp site 3 and IHF site II, is dispensable for FimB recombination but that this region is also required for full amino acid stimulation of inversion. Further work reveals that the region is likely to contain multiple regulatory elements. Lrp site 3 is shown to bind the regulatory protein with low affinity, and a mutation that enhances binding to this element is found both to diminish the stimulatory effects of IVLA on FimB recombination and to inhibit recombination in the absence of the amino acids. The results obtained emphasize the importance of Lrp site 3 as a control element but also highlight the complexity of the regulatory system that affects this site.