Ab initio study of NMR 15N chemical shift differences induced by Ca2+ binding to EF-hand proteins

R. BIEKOFSKY; A.G. TURJANSKI; D. A. ESTRIN; J. FEENEY; A. PASTORE

BIOCHEMISTRY

American Chemical Society

Lugar: Columbus, USA; Año: 2004 vol. 43 p. 6554 - 6564

0006-2960

EF-hands are Ca2+ binding motifs that are widely distributed throughout the entire living organism kingdom. At present, relatively little is known at a quantum mechanical level about the mechanisms that allow Ca2+ to be recognized specifically by EF-hands and to induce a conformational switch from a compact (closed) conformation to an open state that exposes a large patch of hydrophobic residues. Here, we present a study of NMR 15N chemical shifts based on ab initio quantum mechanical calculations carried out on a minimalist model system linking both Ca2+ binding sites across the alpha-sheetof an EF-hand domain. Calculated and experimentally determined chemical shift changes are correlated with structural changes induced upon metal binding. The effect of Ca2+ binding on these 15N shifts can be dissected into two main contributions: one from -polarization of alpha sheet amide groups and the other from rotation of an isoleucine side chain. By correlating this description with experimental evidence, different polarization states for the alpha-sheet amide groups were identified and linked to the overallconformation of different EF-hand domains. When all four alpha-sheet amide groups are polarized, the ab initio calculations in our model indicate a cooperative stabilization effect due to the establishment of a circular network of donor-acceptor interactions connecting the two Ca2+ ions across the â-sheet. The emerging hypothesis from our analysis is that this cooperative network of interactions is essential for stabilizing the open conformation of an EF-hand domain.