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Phytochrome: Protein conformation and associated kinase
Abstract
Phytochrome is the ubiquitous red light photoreceptor in green plants. There are three aspects of phytochrome A (dark grown phytochrome) which are the subject of this study: (i) the conformation the entire protein; its quaternary and zinc chelated structures, (ii) conformation(s) of the N-terminal (6 kDa) domain of phytochrome A, and (iii) the phytochrome associated kinase. The oligomeric content of phytochrome was evaluated by suberimidate crosslinking. It was found that a simple dimeric model of the phytochrome protein is not sufficient. The use of zinc, which apparently binds to the chromophore, as a probe of conformation change has demonstrated a large structural change upon chromophore binding, an unusual result in light of other holoprotein/apoprotein comparisons. This change affects the secondary structure of the protein quite dramatically, but not the quaternary structure. The N-terminal region of phytochrome, a possible receptor binding domain, undergoes a turn-to-helix transition upon photoconversion of phytochrome from the red light absorbing (Pr) to the far-red light absorbing (Pfr) form. Evaluation of this transformation was carried out by both calculation and circular dichroic studies in amphiphilic environments (SDS micelles). It was determined that the N-terminal region (6 kDa) of phytochrome A is capable of forming amphiphilic $\alpha$-helix. The formation of this type of helix upon Pr to Pfr photoconversion is consistent with our present model of phytochrome chromophore-protein interaction. There is a kinase present during later stages of the phytochrome isolation procedure, even with highly purified phytochrome preparations (possible receptor?). It is not known if there is some specific association/interaction between phytochrome and the kinase, or if the association is an "artifact" of isolation. This kinase was purified to homogeneity. The unusually large quantity and subunit composition (compared to other kinases) are discussed. Polyclonal antibody production and internal peptide sequencing are two current approaches we are using to further evaluate the nature of the kinase and its association with phytochrome.
Subject Area
Biochemistry
Recommended Citation
Parker, William Robert, "Phytochrome: Protein conformation and associated kinase" (1992). ETD collection for University of Nebraska-Lincoln. AAI9314426.
https://digitalcommons.unl.edu/dissertations/AAI9314426