Enzymatic activity of the blue light‐regulated phosphodiesterase BlrP1 from <i>Klebsiella pneumoniae</i> shows a nonlinear dependence on light intensity

The blue light-regulated phosphodiesterase BlrP1 from Klebsiella pneumoniae hydrolyzes cyclic dimeric guanosine monophosphate (GMP) in a light-dependent manner. It contains photosensing BLUF domain and functional EAL domain. Previously, it was reported that conformational changes the dimer upon light illumination occurred only when both protomers of were excited. Based on this observation, proposed might be nonlinear intensity sensor. To test this, here, correlation between turnover number hydrolysis reaction (kcat) fraction excited protein (fred) measured by simultaneously monitoring rate fred. Our results show kcat is proportional to fred2. Thus, works as sensor sense strong environment.