Structure and dynamics of Ca2+-binding domain 1 of the Na+/Ca2+ exchanger in the presence and in the absence of Ca2+.
The Na(+)/Ca(2+) exchanger is the major exporter of Ca(2+) across the cell membrane of cardiomyocytes. The activity of the exchanger is regulated by a large intracellular loop that contains two Ca(2+)-binding domains, calcium-binding domain (CBD) 1 and CBD2. CBD1 binds Ca(2+) with much higher affinity than CBD2 and is considered to be the primary Ca(2+) sensor. The effect of Ca(2+) on the structure and dynamics of CBD1 has been characterized by NMR spectroscopy using chemical shifts, residual dipolar couplings, and spin relaxation. Residual dipolar couplings are used in a new way for residue selection in the determination of the anisotropic rotational diffusion tensor from spin relaxation data. The results provide a highly consistent description across these complementary data sets and show that Ca(2+) binding is accompanied by a selective conformational change among the binding site residues. Residues that exhibit a significant conformational change are also sites of altered dynamics. In particular, Ca(2+) binding restricts the mobility of the major acidic segment and affects the dynamics of several nearby binding loops. These observations indicate that Ca(2+) elicits a local transition to a well-ordered coordination geometry in the CBD1-binding site.
Johnson
Eric
E
Department of Chemistry and Biochemistry and National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32306, USA.
Bruschweiler-Li
Lei
L
Showalter
Scott A
SA
Vuister
Geerten W
GW
Zhang
Fengli
F
Brüschweiler
Rafael
R
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry*; D004285:Dogs; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D019831:Sodium-Calcium Exchanger / Q000737:chemistry*
D011994:Recombinant Proteins; D019831:Sodium-Calcium Exchanger; C110374:sodium-calcium exchanger 1; D002118:Calcium