Determinants of Affinity and Activity of the Anti-Sigma Factor AsiA
Joshua M. Gilmore
Ramona J. Bieber Urbauer
Leonid Minakhin
Vladimir Akoyev
Michal Zolkiewski
Konstantin Severinov
Jeffrey L. Urbauer
10.1021/bi1002635.s001
https://acs.figshare.com/articles/journal_contribution/Determinants_of_Affinity_and_Activity_of_the_Anti_Sigma_Factor_AsiA/2748586
The AsiA protein is a T4 bacteriophage early gene product that regulates transcription of host and viral genes. Monomeric AsiA binds tightly to the σ<sup>70</sup> subunit of <i>Escherichia coli</i> RNA polymerase, thereby inhibiting transcription from bacterial promoters and phage early promoters and coactivating transcription from phage middle promoters. Results of structural studies have identified amino acids at the protomer−protomer interface in dimeric AsiA and at the monomeric AsiA−σ<sup>70</sup> interface and demonstrated substantial overlap in the sets of residues that comprise each. Here we evaluate the contributions of individual interfacial amino acid side chains to protomer−protomer affinity in AsiA homodimers, to monomeric AsiA affinity for σ<sup>70</sup>, and to AsiA function in transcription. Sedimentation equilibrium, dynamic light scattering, electrophoretic mobility shift, and transcription activity measurements were used to assess affinity and function of site-specific AsiA mutants. Alanine substitutions for solvent-inaccessible residues positioned centrally in the protomer−protomer interface of the AsiA homodimer, V14, I17, and I40, resulted in the largest changes in free energy of dimer association, whereas alanine substitutions at other interfacial positions had little effect. These residues also contribute significantly to AsiA-dependent regulation of RNA polymerase activity, as do additional residues positioned at the periphery of the interface (K20 and F21). Notably, the relative contributions of a given amino acid side chain to RNA polymerase inhibition and activation (MotA-independent) by AsiA are very similar in most cases. The mainstay for intermolecular affinity and AsiA function appears to be I17. Our results define the core interfacial residues of AsiA, establish roles for many of the interfacial amino acids, are in agreement with the tenets underlying protein−protein interactions and interfaces, and will be beneficial for a general, comprehensive understanding of the mechanistic underpinnings of bacterial RNA polymerase regulation.
2010-07-27 00:00:00
phage middle promoters
T 4 bacteriophage
RNA polymerase activity
AsiA function
acid side chains
monomeric AsiA affinity
interface
RNA polymerase regulation
acid side chain
Escherichia coli RNA polymerase
transcription activity measurements
RNA polymerase inhibition
electrophoretic mobility shift
residue