The PHY domain is required for conformational stability and spectral integrity of the bacteriophytochrome from...

Bacteriophytochrome from Deinococcus radiodurans (DrBphP) is a plant phytochrome homolog. To investigate the interaction of chromophore and protein structure, we purified recombinant DrBphP and performed biochemical analyses. Differences of apo- and holo-protein in electrophoretic properties in native gels and their susceptibility to trypsin indicate changes in both the conformation and surface topography of this protein as a result of chromophore assembly. Furthermore, proteolysis to Pr and Pfr conformers displayed distinctive cleavage patterns with a noticeable Pr-specific tryptic fragment. Of interest, a prolonged tryptic digestion showed a more severe impact upon the Pfr form. Most importantly, when we assessed the extent of dark reversion to evaluate the role of the cleaved part, a rapidly accelerated reversion was observed upon cleavage at residues 329-505 corresponding to the PHY domain. Our data thus show that the PHY domain is necessary for the Pfr stabilization and spectral integrity of DrBphP.