Nuclear magnetic resonance structure of calcium-binding protein 1 in a Ca2+-bound closed state: Implications for target recognition

✍ Scribed by Saebomi Park; Congmin Li; James B. Ames

• Book ID: 105356668
• Publisher: Cold Spring Harbor Laboratory Press
• Year: 2011
• Tongue: English
• Weight: 597 KB
• Volume: 20
• Category: Article
• ISSN: 0961-8368
• DOI: 10.1002/pro.662

✦ Synopsis

Abstract

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 nuclear Overhauser effect 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.