Solution structure of calcium-free calmodulin.
The three-dimensional structure of calmodulin in the absence of Ca2+ has been determined by three- and four-dimensional heteronuclear NMR experiments, including ROE, isotope-filtering combined with reverse labelling, and measurement of more than 700 three-bond J-couplings. In analogy with the Ca(2+)-ligated state of this protein, it consists of two small globular domains separated by a flexible linker, with no stable, direct contacts between the two domains. In the absence of Ca2+, the four helices in each of the two globular domains form a highly twisted bundle, capped by a short anti-parallel beta-sheet. This arrangement is qualitatively similar to that observed in the crystal structure of the Ca(2+)-free N-terminal domain of troponin C.
Kuboniwa
H
H
Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0520, USA.
Tjandra
N
N
Grzesiek
S
S
Ren
H
H
Klee
C B
CB
Bax
A
A
D000818:Animals; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D002147:Calmodulin / Q000737:chemistry* / Q000378:metabolism; D002247:Carbon Isotopes; D007553:Isotope Labeling; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D010649:Phenylalanine / Q000737:chemistry; D011487:Protein Conformation; D012996:Solutions
D002147:Calmodulin; D002247:Carbon Isotopes; D012996:Solutions; D010649:Phenylalanine; D002118:Calcium