1S36

Crystal structure of a Ca2+-discharged photoprotein: Implications for the mechanisms of the calcium trigger and the bioluminescence

Summary for 1S36

• Entry DOI: 10.2210/pdb1s36/pdb
• Related: 1EJ3 1EL4 1JF0 1JF2 1QV0 1QV1
• Descriptor: Obelin, SODIUM ION, CHLORIDE ION, ... (6 entities in total)
• Functional Keywords: photoprotein, obelin, bioluminescence, calcium binding, ef-hand, aequorin, structural genomics, psi, protein structure initiative, southeast collaboratory for structural genomics, secsg, luminescent protein
• Biological source: Obelia longissima
• Total number of polymer chains: 1
• Total formula weight: 22777.86

Authors

Deng, L.,Markova, S.V.,Vysotski, E.S.,Liu, Z.-J.,Lee, J.,Rose, J.,Wang, B.-C.,Southeast Collaboratory for Structural Genomics (SECSG) (deposition date: 2004-01-12, release date: 2004-10-05, Last modification date: 2023-08-23)

Primary citation

Deng, L.,Markova, S.V.,Vysotski, E.S.,Liu, Z.-J.,Lee, J.,Rose, J.,Wang, B.-C.
Crystal structure of a Ca2+-discharged photoprotein: implications for mechanisms of the calcium trigger and bioluminescence
J.Biol.Chem., 279:33647-33652, 2004

PubMed Abstract: Ca2+-regulated photoproteins are members of the EF-hand calcium-binding protein family. The addition of Ca2+ produces a blue bioluminescence by triggering a decarboxylation reaction of protein-bound hydroperoxycoelenterazine to form the product, coelenteramide, in an excited state. Based on the spatial structures of aequorin and several obelins, we have postulated mechanisms for the Ca2+ trigger and for generation of the different excited states that are the origin of the different colors of bioluminescence. Here we report the crystal structure of the Ca2+-discharged photoprotein obelin at 1.96-A resolution. The results lend support to the proposed mechanisms and provide new structural insight into details of these processes. Global conformational changes caused by Ca2+ association are typical of the class of calcium signal modulators within the EF-hand protein superfamily. Accommodation of the Ca2+ ions into the loops of the EF-hands is seen to propagate into the active site of the protein now occupied by the coelenteramide where there is a significant repositioning and flipping of the His-175 imidazole ring as crucially required in the trigger hypothesis. Also the H-bonding between His-22 and the coelenterazine found in the active photoprotein is preserved at the equivalent position of coelenteramide, confirming the proposed rapid excited state proton transfer that would lead to the excited state of the phenolate ion pair, which is responsible for the blue emission of bioluminescence.

PubMed: 15155735
DOI: 10.1074/jbc.M402427200

Experimental method

X-RAY DIFFRACTION (1.96 Å)