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Structural basis for the observed differential magnetic anisotropic tensorial values in calcium binding proteins
Author(s) -
Mustafi Sourajit M.,
Mukherjee Sulakshana,
Chary Kandala V. R.,
Cavallaro Gabriele
Publication year - 2006
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.21121
Subject(s) - heteronuclear molecule , spins , anisotropy , paramagnetism , crystallography , chemistry , calcium binding protein , lanthanide , calcium , ion , nuclear magnetic resonance , condensed matter physics , nuclear magnetic resonance spectroscopy , physics , stereochemistry , organic chemistry , quantum mechanics
Lanthanide ions (Ln 3+ ), which have ionic radii similar to those of Ca 2+ , can displace the latter in a calcium binding protein, without affecting its tertiary structure. The paramagnetic Ln 3+ possesses large anisotropic magnetic susceptibilities and produce pseudocontact shifts (PCSs), which have r −3 dependence. The PCS can be seen for spins as far as 45 Å from the paramagnetic ion. They aid in structure refinement of proteins by providing long‐range distance constraints. Besides, they can be used to determine the interdomain orientation in multidomain proteins. This is particularly important in the context of a calcium binding protein from Entamoeba histolytica ( Eh CaBP), which consists of two globular domains connected by a flexible linker region containing 8 residues. As a first step to obtain the interdomain orientation in Eh CaBP, a suite of 2D and 3D heteronuclear experiments were recorded on Eh CaBP by displacing calcium with Ce 3+ , Ho 3+ , Er 3+ , Tm 3+ , Dy 3+ , and Yb 3+ ions in separate experiments, and the PCS of 1 H N and 15 N spins were measured. Such data have been used in the refinement of the individual domain structures of the protein in parallel with the calculation of the respective magnetic anisotropy tensorial values, which differ substantially (2.1–2.8 times) from what is found in other Ca 2+ binding loops. This study provides a structural basis for such variations in the magnetic anisotropy tensorial values. Proteins 2006. © 2006 Wiley‐Liss, Inc.