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Abstract
The general stress response of Bacillus subtilis can be activated by stimuli such as the addition of salt or ethanol and with blue light. In the latter response, YtvA activates sigma(B) through a cascade of Rsb proteins, organized in stressosomes. YtvA is composed of an N-terminal LOV (light, oxygen, and voltage) domain and a C-terminal STAS (sulfate transporter and anti-sigma factor) domain and shows light-modulated GTP binding in vitro. Here, we examine the mechanism of YtvA-mediated activation of sigma(B) in vivo with site-directed mutagenesis. Constitutive off and constitutive on mutations have been identified. Disruption of GTP binding in the STAS domain eliminates light activation of sigma(B). In contrast, modification of sites relevant for phosphorylation of STAS domains does not affect the stress response significantly. The data obtained are integrated into a model for the structure of full-length YtvA, which presumably functions as a dimer.
Highlights
The general stress response of Bacillus subtilis can be activated by stimuli such as the addition of salt or ethanol and with blue light
We focus on three regions of the protein, the flavinbinding pocket, the -sheet of the LOV domain, and the GTPbinding site, and on potential phosphorylation sites of the STAS domain
Based on electron microscopy data of reconstituted stressosomes, Marles-Wright et al (16) recently postulated that the RsbR paralogs from B. subtilis, including YtvA, are incorporated into stressosomes as dimers, such that STAS domain dimers form the core of the stressosome, to which the dimeric N-terminal domain is linked via a helical region
Summary
It has been demonstrated in vitro that YtvA shows light-dependent GTP binding, presumably at its NTP-binding site in the STAS domain (20). A conserved glutamine, which is in hydrogen-bonding contact with the isoalloxazine ring of FMN, rotates its side chain by 180o upon covalent adduct formation (21) Replacement of this residue by leucine in the LOV2 domain of Phy from Adiantum results in a considerable reduction of the light-induced structural change (22). We focus on three regions of the protein, the flavinbinding pocket, the -sheet of the LOV domain, and the GTPbinding site, and on potential phosphorylation sites of the STAS domain.
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