Monitoring the transition from the T to the R state in E.coli aspartate transcarbamoylase by X-ray crystallography: crystal structures of the E50A mutant enzyme in four distinct allosteric states.
A detailed description of the transition that allosteric enzymes undergo constitutes a major challenge in structural biology. We have succeeded in trapping four distinct allosteric states of a mutant enzyme of Escherichia coli aspartate transcarbomylase and determining their structures by X-ray crystallography. The mutant version of aspartate transcarbamoylase in which Glu50 in the catalytic chains was replaced by Ala destabilizes the native R state and shifts the equilibrium towards the T state. This behavior allowed the use of substrate analogs such as phosphonoacetamide and malonate to trap the enzyme in T-like and R-like structures that are distinct from the T-state structure of the wild-type enzyme (as represented by the structure of the enzyme with CTP bound and the R-state structure as represented by the structure with N-(phosphonacetyl)-L-aspartate bound). These structures shed light on the nature and the order of internal structural rearrangements during the transition from the T to the R state. They also suggest an explanation for diminished activity of the E50A enzyme and for the change in reaction mechanism from ordered to random for this mutant enzyme.
Department of Chemistry, Merkert Chemistry Center, Boston College, Chestnut Hill, MA 02467, USA.
Kimberly
K
Stieglitz
Boguslaw
B
Stec
Darren P
DP
Baker
Evan R
ER
Kantrowitz
D000495:Allosteric Site; D001221:Aspartate Carbamoyltransferase / Q000737:chemistry*; D001665:Binding Sites; D020134:Catalytic Domain; D018360:Crystallography, X-Ray / Q000379:methods*; D004926:Escherichia coli / Q000201:enzymology*; D008024:Ligands; D008314:Malonates / Q000737:chemistry; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009943:Organophosphorus Compounds / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012492:Salts / Q000737:chemistry; D013329:Structure-Activity Relationship; D014965:X-Rays
D008024:Ligands; D008314:Malonates; D009943:Organophosphorus Compounds; D012492:Salts; C063084:phosphonoacetamide; C030290:malonic acid; D001221:Aspartate Carbamoyltransferase