On the Binding of BODIPY-GTP by the Photosensory Protein YtvA from the Common Soil Bacterium Bacillus subtilis

The YtvA protein, which is one of the proteins that comprises the network carrying out the signal transfer inducing the general stress response in Bacillus subtilis, is composed of an N-terminal LOV domain (that binds a flavin [FMN]) and a C-terminal STAS domain. This latter domain shows sequence features typical for a nucleotide (NTP) binding protein. It has been proposed (FEBS Lett., 580 [2006], 3818) that BODIPY-GTP can be used as a reporter for nucleotide binding to this site and that activation of the LOV domain by blue light is reflected in an alteration of the BODIPY-GTP fluorescence. Here we confirm that BODIPY-GTP indeed binds to YtvA, but rather nonspecifically, and not limited to the STAS domain. Blue-light modulation of fluorescence emission of YtvA-bound BODIPY-GTP is observed both in the full-length YtvA protein and in a truncated protein composed of the LOV-domain plus the LOV-STAS linker region (YtvA(1-147)) as a light-induced decrease in fluorescence emission. The isolated LOV domain (i.e. without the linker region) does not show such BODIPY-GTP fluorescence changes. Dialysis experiments have confirmed the blue-light-induced release of BODIPY-GTP from YtvA.