Constitutive Activation of Two-Component Response Regulators: Characterization of VirG Activation inAgrobacterium tumefaciens

Abstract

Response regulators are the ultimate modulators in two-component signal transduction pathways. The N-terminal receiver domains generally accept phosphates from cognate histidine kinases to control output. VirG for example, the response regulator of the VirA/VirG two-component system in Agrobacterium tumefaciens, mediates the expression of virulence genes in response to plant host signals. Response regulators have a highly conserved structure and share a similar conformational activation upon phosphorylation, yet the sequence and structural features that determine or perturb the cooperative activation events are ill defined. Here we use VirG and the unique features of the Agrobacterium system to extend our understanding of the response regulator activation. Two previously isolated constitutive VirG mutants, VirGN54D and VirGI77V/D52E, provide the foundation for our studies. In vivo phosphorylation patterns establish that VirGN54D is able to accumulate phosphates from small-molecule phosphate donors, such as acetyl phosphate, while the VirGI77V/D52E allele carries conformational changes mimicking the active conformation. Further structural alterations on these two alleles begin to reveal the changes necessary for response regulator activation.

Atypical OmpR/PhoB Subfamily Response Regulator GlnR of Actinomycetes Functions as a Homodimer, Stabilized by the Unphosphorylated Conserved Asp-focused Charge Interactions

“…Usually the Glu/Ala mutation at the conserved phospho-accepting Asp residue is known to mimic the phosphorylation/ unphosphorylation status of the RRs (45,46), although exceptions do exist. For instance, the Asp 3 Glu mutant of VirG, an RR of the VirA/VirG two-component system in Agrobacterium tumefaciens, does not mimic the phenotype of the phosphorylated VirG.…”

The Atypical OmpR/PhoB Response Regulator ChxR from Chlamydia trachomatis Forms Homodimers In Vivo and Binds a Direct Repeat of Nucleotide Sequences

“…The mutations that resulted in a significant (P Ͻ 0.05) reduction of DNA-interaction are denoted by an asterisk. (3,18,27,40). However, the ability of ChxR to maintain a homodimer conformation and interact with DNA is not the result of this single substitution (D49E).…”

“…ChxR is unique in this respect because the amino acid in the predicted position of the conserved Asp is a Glu residue (E49) (28). Many transcription factors that are activated by a phosphorylated Asp can be converted into a phosphoryl-independent constitutively active state via substitution with Glu (3,18,27,40). Based upon these observations, it was hypothesized that Glu 49 is critical to DNA binding and transcriptional activity of ChxR and that conversion to an Asp could render the molecule inactive.…”

Salmonella Typhimurium general virulence factors: A battle of David against Goliath?

“…Due to the wide range of the sensor ligand-binding domain reported, Salmonella can modulate the gene expression under different environmental changes (Anantharaman & Aravind, 2000;Galperin, Nikolskaya, & Koonin, 2001;Zhulin, Taylor, & Dixon, 1997). The response regulator (RR) produces, through its conserved aspartate phosphorylation, the adaptive response of bacterial cells modulating transcription of certain genes or operons (Gao, Mukhopadhyay, Fang, & Lynn, 2006;Stock et al, 2000).…”