Premium
All three Ca 2+ ‐binding loops of photoproteins bind calcium ions: The crystal structures of calcium‐loaded apo‐aequorin and apo‐obelin
Author(s) -
Deng Lu,
Vysotski Eugene S.,
Markova Svetlana V.,
Liu ZhiJie,
Lee John,
Rose John,
Wang BiCheng
Publication year - 2005
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.041142905
Subject(s) - photoprotein , aequorin , calcium , chemistry , crystallography , ef hand , calcium binding protein , biophysics , stereochemistry , biology , organic chemistry
The crystal structures of calcium‐loaded apoaequorin and apo‐obelin have been determined at resolutions 1.7 Å and 2.2 Å, respectively. A calcium ion is observed in each of the three EF‐hand loops that have the canonical calcium‐binding sequence, and each is coordinated in the characteristic pentagonal bipyramidal configuration. The calcium‐loaded apo‐proteins retain the same compact scaffold and overall fold as the unreacted photoproteins containing the bound substrate, 2‐hydroperoxycoelenterazine, and also the same as the Ca 2+ ‐discharged obelin bound with the product, coelenteramide. Nevertheless, there are easily discerned shifts in both helix and loop regions, and the shifts are not the same between the two proteins. It is suggested that these subtle shifts are the basis of the ability of these photoproteins to sense Ca 2+ concentration transients and to produce their bioluminescence response on the millisecond timescale. A mechanism of intrastructural transmission of the calcium signal is proposed.