Cloning, purification, structural, and functional characterization of methicillin-resistant Staphylococcus aureus (MRSA252) RsbV protein

The Critical Roles of Conserved Glu 21 and Asp 23 of a Staphylococcal Anti-Anti-Sigma Factor

Staphylococcus aureus and similar bacteria cope with stressful environments using a set of conserved proteins including σB, an alternative sigma factor. The initiation of transcription by σB is obstructed by RsbW, an anti-sigma factor. RsbW also associates and phosphorylates RsbV, an anti-anti-sigma factor. A modeling study previously suggested that Glu 21, Asp 23, and Tyr 54 of S. aureus RsbV form non-covalent bonds with Arg 23, an indispensable residue of cognate RsbW. Herein, we have noted that Glu 21, and Asp 23 are conserved residues, whereas Tyr 54 is a semi-conserved residue. Additionally, our MD simulation studies indicate that both Glu 21 and Asp 23 may maintain the structure of RsbV. To verify the computational data, two RsbV mutants, created by replacing Glu 21 and Asp 23 with an Ala residue, were elaborately investigated using some in vitro tools. The results reveal that both the above residues are critical for preserving the structure of RsbV. Interestingly, the RsbV mutant harboring Ala at position 23 was very little phosphorylated by RsbW. This mutant, compared to the RsbV mutant carrying Ala at position 21, also showed a weaker interaction with RsbW. The ways Glu 21 and Asp 23 keep various properties of RsbV intact have been discussed at length.

A conserved arginine residue in a staphylococcal anti-sigma factor is required to preserve its kinase activity, structure, and stability

RsbW, σ^B, and RsbV, encoded by Staphylococcus aureus and related bacteria, act as an anti-sigma factor, an sigma factor, and an anti-anti-sigma factor, respectively. The interaction between RsbW and σ^B blocks the transcription initiation activity of the latter protein. RsbW also functions as a serine kinase and phosphorylates RsbV in the presence of ATP. Our modeling study indicates that the RsbW-RsbV complex is stabilized by twenty-four intermolecular non-covalent bonds. Of the bond-forming RsbW residues, Arg 23, and Glu 49 are conserved residues. To understand the roles of Arg 23 in RsbW, rRsbW[R23A], a recombinant S. aureus RsbW (rRsbW) harboring Arg to Ala change at position 23, was investigated using various probes. The results reveal that rRsbW[R23A], like rRsbW, exists as the dimers in the aqueous solution. However, rRsbW[R23A], unlike rRsbW, neither interacted with a chimeric RsbV (rRsbV) nor formed the phosphorylated rRsbV in the presence of ATP. Furthermore, the tertiary structure and hydrophobic surface area of rRsbW[R23A] matched little with those of rRsbW. Conversely, both rRsbW[R23A] and rRsbW showed interaction with a recombinant σ^B (rσ^B). rRsbW and rRsbW[R23A] were also unfolded via the formation of at least one intermediate in the presence of urea. However, the thermodynamic stability of rRsbW significantly differed from that of rRsbW[R23A]. Our molecular dynamics (MD) simulation study also reveals the substantial change of structure, dimension, and stability of RsbW due to the above mutation. The ways side chain of critical Arg 23 contributes to maintaining the tertiary structure, and stability of RsbW was elaborately discussed.Communicated by Ramaswamy H. Sarma.