Spectral properties of phytochrome Agp2 from Agrobacterium tumefaciens are specifically modified by a compound of the cell extract.
Phytochromes are widely distributed photoreceptors that are converted by light between the red absorbing Pr and the far-red absorbing Pfr form. The soil bacterium Agrobacterium tumefaciens contains two phytochromes, Agp1 and Agp2, which act as light-regulated histidine kinases. Whereas most phytochromes are stable in the Pr form, Agp2 and few other phytochromes convert into Pfr in darkness. We have shown in a previous publication that the spectral properties of recombinant Agp2 are modified by compounds of the cell extract from an Agrobacterium agp1(-)/agp2(-) double knockout mutant. In the present work we performed concentration series which show that the interaction is specific and that the modifying factor has a concentration of ca. 0.2 microM. We have also performed a series of mixing experiments with the truncated protein Agp2-M2, which consists of the N-terminal chromophore module (501 amino acids). The cell extract inhibited the photoconversion of Agp2-M2 in an unspecific way. In concentration series, this negative effect was less pronounced when lower concentrations of Agp2-M2 were used. In the presence of excess Agp2-M2 apoprotein, the cell extract did no longer modify the spectral properties of Agp2. The data suggest that the factor of the cell extract interacts specifically with the N-terminal moiety of Agp2.
Krieger
Alexander
A
Freie Universität Berlin, Pflanzenphysiologie, Königin Luise Strasse 12-16, D-14195 Berlin, Germany.
Molina
Isabel
I
Oberpichler
Inga
I
Michael
Norbert
N
Lamparter
Tilman
T
D016960:Agrobacterium tumefaciens / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000528:radiation effects; D003001:Cloning, Molecular; D003624:Darkness; D017353:Gene Deletion; D007700:Kinetics; D008027:Light; D010834:Phytochrome / Q000737:chemistry* / Q000235:genetics / Q000528:radiation effects; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000528:radiation effects; D013053:Spectrophotometry
D001426:Bacterial Proteins; D011994:Recombinant Proteins; D010834:Phytochrome