Protein conformational changes of Agrobacterium phytochrome Agp1 during chromophore assembly and photoconversion.
Phytochromes are widely distributed photochromic biliprotein photoreceptors. Typical bacterial phytochromes such as Agrobacterium Agp1 have a C-terminal histidine kinase module; the N-terminal chromophore module induces conformational changes in the protein that lead to modulation of kinase activity. We show by protein cross-linking that the C-terminal histidine kinase module of Agp1 mediates stable dimerization. The fragment Agp1-M15, which comprises the chromophore module but lacks the histidine kinase module, can also form dimers. In this fragment, dimer formation was stronger for the far-red-absorbing form Pfr than for the red-absorbing form Pr. The same or similar behavior was found for Agp1-M15Delta9N and Agp1-M15Delta18N, which lack 9 and 18 amino acids of the N-terminus, respectively. The fragment Agp1-M20, which is derived from Agp1-M15 by truncation of the C-terminal "PHY domain" (191 amino acids), can also form dimers, but dimerization is independent of irradiation conditions. The cross-linking data also showed that the PHY domain is in tight contact with Lys 16 of the protein and that the nine N-terminal amino acids mediate oligomer formation. Limited proteolysis shows that the hinge region between the chromophore module and the histidine kinase and a part of the PHY domain become exposed upon Pr to Pfr photoconversion.
Noack
Steffi
S
Pflanzenphysiologie, Freie Universität Berlin, Königin Luise Strasse 12-16, D-14195 Berlin, Germany.
Michael
Norbert
N
Rosen
Ran
R
Lamparter
Tilman
T
D002850:Chromatography, Gel; D003432:Cross-Linking Reagents; D005976:Glutaral / Q000737:chemistry; D000071677:Histidine Kinase; D008958:Models, Molecular; D020283:Photoreceptors, Microbial / Q000096:biosynthesis / Q000528:radiation effects; D010834:Phytochrome / Q000737:chemistry* / Q000528:radiation effects; D011487:Protein Conformation; D011494:Protein Kinases / Q000502:physiology; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000737:chemistry / Q000528:radiation effects; D012231:Rhizobium / Q000737:chemistry
D003432:Cross-Linking Reagents; D020283:Photoreceptors, Microbial; D011994:Recombinant Proteins; D010834:Phytochrome; D011494:Protein Kinases; D000071677:Histidine Kinase; D005976:Glutaral