Solution NMR structure of GATase subunit and structural basis of interaction between GATase and ATPPase subunits in a two-subunit-type GMPS from Methanocaldococcus jannaschii.
Related Articles Solution NMR structure of GATase subunit and structural basis of interaction between GATase and ATPPase subunits in a two-subunit-type GMPS from Methanocaldococcus jannaschii.
Biochemistry. 2013 May 31;
Authors: Ali R, Kumar S, Balaram H, Sarma SP
Abstract
The solution structure of the monomeric glutamine amidotransferase (GATase) subunit of the Methanocaldococcus janaschii (Mj) guanosine monophosphate synthase (GMPS) has been determined using high-resolution nuclear magnetic resonance methods. Gel filtration chromatography and 15N backbone relaxation studies have shown that Mj GATase subunit is present in solution as a 21 kDa (188 residues) monomer. The ensemble of twenty lowest energy structures showed an rmsd of 0.35±0.06 Å for backbone and 0.8±0.06 Å for all heavy atoms. Furthermore, 99.4 % backbone dihedral angles are present in allowed region of the Ramachandran map, indicating the stereochemical quality of the structure. The tertiary structure of the GATase is composed of a seven-stranded mixed ?-sheet that is fenced by five ?-helices. The Mj GATase is similar in structure to the Pyrococcus horikoshi (Ph) GATase subunit. NMR chemical shift perturbation and changes in line width were monitored to identify residues on GATase that were responsible for interaction with magnesium and the ATPPase subunit respectively. These interaction studies showed that a common surface exists for the metal-ion binding as well as for the protein-protein interaction. The dissociation constant for the GATase-Mg2+ interaction has been found to be ~1mM, which implies that interaction is very weak and falls in fast chemical exchange regime. The GATase-ATPPase interaction on the other hand falls in intermediate chemical exchange regime on NMR time scale. The implication of this interaction on the regulation of the GATase activity of holo GMPS is discussed.
PMID: 23724776 [PubMed - as supplied by publisher]
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