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Novel protein and Mg 2+ configurations in the Mg 2+ GDP complex of the SRP GTPase ffh
Author(s) -
Focia Pamela J.,
Alam Hena,
Lu Thanh,
Ramirez Ursula D.,
Freymann Douglas M.
Publication year - 2003
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.10598
Subject(s) - gtpase , gtp' , signal recognition particle , chemistry , small gtpase , crystallography , biophysics , coordination sphere , protein subunit , magnesium , protein structure , g protein , stereochemistry , biochemistry , signal transduction , biology , peptide sequence , crystal structure , enzyme , signal peptide , gene , organic chemistry
Ffh is the signal sequence recognition and targeting subunit of the prokaryotic signal recognition particle (SRP). Previous structural studies of the NG GTPase domain of Ffh demonstrated magnesium‐dependent and magnesium‐independent binding conformations for GDP and GMPPNP that are believed to reflect novel mechanisms for exchange and activation in this member of the GTPase superfamily. The current study of the NG GTPase bound to Mg 2+ GDP reveals two new binding conformations—in the first the magnesium interactions are similar to those seen previously, however, the protein undergoes a conformational change that brings a conserved aspartate into its second coordination sphere. In the second, the protein conformation is similar to that seen previously, but the magnesium coordination sphere is disrupted so that only five oxygen ligands are present. The loss of the coordinating water molecule, at the position that would be occupied by the oxygen of the γ‐phosphate of GTP, is consistent with that position being privileged for exchange during phosphate release. The available structures of the GDP‐bound protein provide a series of structural snapshots that illuminate steps along the pathway of GDP release following GTP hydrolysis. Proteins 2004;54:000–000. © 2003 Wiley‐Liss, Inc.