Structural and functional features of Crl proteins and identification of conserved surface residues required for interaction with the RpoS/{sigma}S subunit of RNA polymerase

In many γ-proteobacteria, the RpoS/σS sigma factor associates with the core RNA polymerase (RNAP) to modify global gene transcription in stationary phase and under stress conditions. The small regulatory protein Crl stimulates the association of σS with the core RNAP in Escherichia coli and Salmonella enterica serovarTyphimurium (S. Typhimurium), through direct and specific interaction with σS. The structural determinants of Crl involved in σS binding are unknown. Here, we report the X-ray crystal structure of the Proteus mirabilis Crl protein (CrlPM) and a structural model for S. Typhimurium Crl (CrlSTM). Using a combination of in vivo and in vitro assays, we demonstrated that CrlSTM and CrlPM are structurally similar and perform the same biological function. In the Crl structure, a cavity enclosed by flexible arms contains two patches of conserved and exposed residues required for σS binding. Among these, charged residues likely to be involved in electrostatic interactions driving Crl-σS complex formation were identified. CrlSTM and CrlPM interact with domain 2 of σS with the same binding properties as with full-length σS. These results suggest that Crl family members share a common mechanism of σS binding in which the flexible arms of Crl might play a dynamic role.

Source: BJ Gene - July 24, 2014 Category: Biochemistry Authors: P Cavaliere, F Levi-Acobas, C Mayer, F A Saul, P England, P Weber, B Raynal, V Monteil, J Bellalou, A Haouz, F Norel Tags: BJ Gene Source Type: research