1UHI

Crystal structure of i-aequorin

Summary for 1UHI

• Entry DOI: 10.2210/pdb1uhi/pdb
• Related: 1EJ3 1EL4 1JF2 1UHH 1UHJ 1UHK
• Descriptor: Aequorin 2, (2R)-8-BENZYL-2-HYDROPEROXY-6-(4-HYDROXYPHENYL)-2-(4-IODOBENZYL)-7,8-DIHYDROIMIDAZO[1,2-A]PYRAZIN-3(2H)-ONE (3 entities in total)
• Functional Keywords: 4 ef-hand motif, complex, luminescent protein
• Biological source: Aequorea victoria
• Total number of polymer chains: 2
• Total formula weight: 44451.11

Authors

Toma, S.,Chong, K.T.,Nakagawa, A.,Teranishi, K.,Inouye, S.,Shimomura, O. (deposition date: 2003-07-03, release date: 2005-02-08, Last modification date: 2023-10-25)

Primary citation

Toma, S.,Chong, K.T.,Nakagawa, A.,Teranishi, K.,Inouye, S.,Shimomura, O.
The crystal structures of semi-synthetic aequorins
Protein Sci., 14:409-416, 2005

PubMed Abstract: The photoprotein aequorin emits light by an intramolecular reaction in the presence of a trace amount of Ca(2+). Semi-synthetic aequorins, produced by replacing the coelenterazine moiety in aequorin with the analogues of coelenterazine, show widely different sensitivities to Ca(2+). To understand the structural basis of the Ca(2+)-sensitivity, we determined the crystal structures of four semi-synthetic aequorins (cp-, i-, br- and n-aequorins) at resolutions of 1.6-1.8 A. In general, the protein structures of these semi-synthetic aequorins are almost identical to native aequorin. Of the four EF-hand domains in the molecule, EF-hand II does not bind Ca(2+), and the loop of EF-hand IV is clearly deformed. It is most likely that the binding of Ca(2+) with EF-hands I and III triggers luminescence. Although little difference was found in the overall structures of aequorins investigated, some significant differences were found in the interactions between the substituents of coelenterazine moiety and the amino acid residues in the binding pocket. The coelenterazine moieties in i-, br-, and n-aequorins have bulky 2-substitutions, which can interfere with the conformational changes of protein structure that follow the binding of Ca(2+) to aequorin. In cp-aequorin, the cyclopentylmethyl group that substitutes for the original 8-benzyl group does not interact hydrophobically with the protein part, giving the coelenterazine moiety more conformational freedom to promote the light-emitting reaction. The differences of various semi-synthetic aequorins in Ca(2+)-sensitivity and reaction rate are explained by the capability of the involved groups and structures to undergo conformational changes in response to the Ca(2+)-binding.

PubMed: 15632284
DOI: 10.1110/ps.041067805

Experimental method

X-RAY DIFFRACTION (1.8 Å)