1dgd
AN ALKALI METAL ION SIZE-DEPENDENT SWITCH IN THE ACTIVE SITE STRUCTURE OF DIALKYLGLYCINE DECARBOXYLASE
Structural highlights
FunctionDGDA_BURCE The dialkylglycine decarboxylase is of interest because it normally catalyzes both decarboxylation and amino transfer. It may be more properly described as a decarboxylating aminotransferase rather than an aminotransferring decarboxylase. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe pyridoxal 5'-phosphate-dependent enzyme dialkylglycine decarboxylase (DGD) is activated by K+ and Rb+ ions, whereas Li+ and Na+ ions are inhibitory. A binding site for alkali metal ions close to the active site (site 1) was discovered in the crystal structure of DGD, and an exchange of K+ for Na+ at this site was shown to affect the conformation of two active site residues [Toney, M. D., Hohenester, E., Cowan, S. W., & Jansonius, J. N. (1993) Science 261, 756-759]. We have investigated the effects of alkali metal ions on DGD activity and have determined the crystal structures at 2.8 A resolution of DGD with Li+ and Rb+ bound at site 1. Due to the weak scattering of the Li+ ion, its position had to be modeled using information from small molecule structures. A comparison of the DGD structures with Li+, Na+, K+, and Rb+ bound at site 1 reveals a striking correlation between active site structure and enzymatic activity. The small, inhibitory ions Li+ and Na+ are accommodated by replacing two protein-derived ligands of the larger, activating ions K+ and Rb+ by a single water molecule. This actuates a two-state structural switch between active and inactive enzyme that involves a concerted reorientation of the active site residues Ser80 and Tyr301 and a small change in the quaternary structure of the DGD tetramer. An important role of the essential K+ ion in both cofactor binding and the organization of a catalytically competent active site structure is proposed. In the structure of DGD with Rb+ bound at site 1, a second Rb+ ion has partially replaced the structural Na+ ion at metal binding site 2 on the surface of the DGD molecule, without significantly altering the protein structure. In contrast to Na+, the Rb+ ion is bound with unfavorable geometry, and it is proposed that the rigid site 2 structure results in a pronounced selectivity for Na+ ions. An alkali metal ion size-dependent switch in the active site structure of dialkylglycine decarboxylase.,Hohenester E, Keller JW, Jansonius JN Biochemistry. 1994 Nov 22;33(46):13561-70. PMID:7947767[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References | ||||||||||||||||||||
