Blue news: NTP binding properties of the blue‐light sensitive YtvA protein from Bacillus subtilis

The blue‐light sensitive protein YtvA from Bacillus subtilis is built of a photoactive, flavin‐binding LOV (Light, Oxygen and Voltage) domain and a STAS domain with unknown function. Here we show that YtvA binds a fluorescent derivative of guanosine triphosphate (GTP TR ) that can be displaced by both GTP or ATP. Unspecific NTP (N = G or A) binding is supported by the molecular model of YtvA‐STAS. Blue‐light activation of YtvA results in small and dark‐reversible spectroscopic changes for GTP TR , suggesting that light‐driven conformational changes are transmitted from the LOV core to the GTP TR binding site. These results support the idea that STAS domains may have a general NTP binding role and open a way to investigate the molecular functionality of YtvA‐STAS.