A study of Escherichia coli adenylosuccinate synthetase association states and the interface residues of the homodimer

作者：Wang WY; Gorrell A; Honzatko RB; Fromm HJ

来源：Journal of Biological Chemistry, 1997, 272(11): 7078-7084.

The state of aggregation of adenylosuccinate synthetase from Escherichia coli is a point of controversy, with crystal structures indicating a dimer and some solution studies indicating a monomer, Crystal structures implicate Arg(143) and Asp(231) in stabilizing the dimer, with Arg(143) interacting directly with bound IMP of the a fold related subunit, Residue Arg(143) was changed to Lys and Leu, and residue Asp(231) was changed to Ala. Matrix-assisted laser desorption ionization mass spectroscopy and analytical ultracentrifugation of the wild-type and the mutant enzymes indicate a mixture of monomers and dimers, with a majority of the enzyme in the monomeric state, In the presence of active site ligands, the wild-type enzyme exists almost exclusively as a dimer, whereas the mutant enzymes show only slightly decreased dissociation constants for the dimerization, Initial rate kinetic studies of the wild-type and mutant enzymes show similar K-cat and K-m values for aspartate, However, increases in the K-m values of GTP and IMP are observed for the mutant, Changes in dissociation constants for IMP are comparable with changes in K-m, values, Our results suggest that IMP binding induces enzyme dimerization and that two residues in the interface region, Arg(143) and Asp(231), play significant roles in IMP and GTP binding.

• 出版日期1997-3-14