Solution structure of calcium-free calmodulin

Abstract

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.

An interaction‐based analysis of calcium‐induced conformational changes in Ca2+ sensor proteins

“…Complementary insights were also obtained from a corresponding analysis of TnC, made by comparing the apo N-terminal domain from the X-ray crystal structure (Satyshur et al, 1994) and the N-terminal domain from the Ca2+-loaded NMR structure (Slupsky & Sykes, 1995). In all cases, the comparisons of the closed and open conformations confirm that Ca2+ binding causes opening within each of the EF-hands, as first predicted by the HMJ model based on the crystal structure of TnC (Herzberg et al, 1986), and subsequently confirmed by NMR solution structures of CaM and TnC (Finn et al, 1995;GagnC et al, 1995;Kuboniwa et al, 1995;Zhang et al, 1995).…”

“…However, the two proteins have strikingly different conformations in the Ca'+-loaded state. CaM undergoes a large Ca'+-induced conformational change (Finn et al, 1995;Kuboniwa et al, 1995;Zhang et al, 1995). whereas Ca2+ binding has a much smaller effect on the calbindin Dgk structure, and does not lead to exposure of a large hydrophobic surface (Szebenyi & Moffat, 1986;Skelton et al, 1994).…”

“…a representative non-sensor protein, has been reported previously (Akke et al, 1995;Skelton et al, 1995). The general features of Ca'+-induced conformational changes in CaM and TnC were described when the structures of their apo state were first reported (Finn et al, 1995;Gagnt et al, 1995;Kuboniwa et al, 1995;Zhang et al, 1995). However, these descriptions did not reveal the underlying structural basis for the response to Ca2+ binding.…”

Protein-metal interactions of calmodulin and α-synuclein monitored by selective noncovalent adduct protein probing mass spectrometry

“…Each globular domain has two EF-hand structural motifs, which are high affinity binding sites for Ca 2ϩ ions [53][54][55]. Figure 1a shows the mass spectrum obtained from a solution containing apocalmodulin and 18C6.…”

Intermolecular tuning of calmodulin by target peptides and proteins: Differential effects on Ca2+ binding and implications for kinase activation

“…CaM has a dumbbell shaped structure in which two domains, termed the N and C domains, are linked by a flexible helix (Taylor et al, 1991;Finn et al, 1995;Kuboniwa et al, 1995;Zhang et al, 1995). Each domain binds two Ca2+ ions into a pair of EF-hand type sites.…”