NMR structure of CaBP1 in a Ca(2+) -bound closed state: Implications for target recognition.

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NMR structure of CaBP1 in a Ca(2+) -bound closed state: Implications for target recognition.

NMR structure of CaBP1 in a Ca(2+) -bound closed state: Implications for target recognition.

Protein Sci. 2011 May 23;

Authors: Park S, Li C, Ames JB

Calcium binding protein 1 (CaBP1), a neuron-specific member of the calmodulin (CaM) superfamily, regulates the Ca(2+) dependent activity of inositol 1,4,5-triphosphate receptors (InsP3Rs) and various voltage-gated Ca(2+) channels. Here we present the NMR structure of full-length CaBP1 with Ca(2+) bound at the first, third and fourth EF-hands. A total of 1250 NOE distance measurements and 70 residual dipolar coupling restraints define the overall main chain structure with a root-mean-squared deviation of 0.54 Å (N-domain) and 0.48 Å (C-domain). The first 18 residues from the N-terminus in CaBP1 (located upstream of the first EF-hand) are structurally disordered and solvent exposed. The Ca(2+) -saturated CaBP1 structure contains two independent domains separated by a flexible central linker similar to that in calmodulin and troponin C. The N-domain structure of CaBP1 contains two EF-hands (EF1 and EF2) both in a closed conformation (interhelical angles = 129° (EF1) and 142° (EF2)). The C-domain contains EF3 and EF4 in the familiar Ca(2+) -bound open conformation (interhelical angles = 105° (EF3) and 91° (EF4)). Surprisingly, the N-domain adopts the same closed conformation in the presence or absence of Ca(2+) bound at EF1. The Ca(2+) -bound closed conformation of EF1 is reminiscent of Ca(2+) -bound EF-hands in a closed conformation found in cardiac troponin C and calpain. We propose that the Ca(2+) -bound closed conformation of EF1 in CaBP1 might undergo an induced-fit opening only in the presence of a specific target protein, and thus may help explain the highly specialized target binding by CaBP1.

PMID: 21608059 [PubMed - as supplied by publisher]



Source: PubMed