Effects of hydrostatic pressure on the conformational equilibrium of tryptophan synthase from Salmonella typhimurium.
A wide range of parameters influence allosteric communications between the alpha- and beta-subunits of the Trp synthase alpha(2)beta(2) multienzyme complex with L-Ser, including monovalent cations, pH, temperature, ligands, organic solvents, and hydrostatic pressure. The conformational change from closed to open can be monitored either by absorbance at 423 nm or fluorescence at 495 nm from the pyridoxal-5'-phosphate-L-Ser complex. Pressure perturbation was used to quantify the effects of monovalent cations, ligands, and mutations on the conformational equilibrium of Trp synthase. P-jump kinetics in the presence of Na(+), NH(4) (+), and Na(+) together with benzimidazole were also examined. The plots of lnk versus P are nonlinear and require a compressibility (beta(double dagger) (o)) term to obtain a good fit. beta(double dagger) (o) is positive for the Na(+) enzyme but negative for NH(4) (+) and Na(+) with benzimidazole. These results suggest that there is a large contribution of solvation to the kinetics of the conformational change of Trp synthase. The relaxation kinetics are also different if the P-jumps are made by increasing or decreasing pressure, suggesting that the enzyme conformations are ensembles of microstates.
Department of Chemistry, University of Georgia, Athens, 30602, USA. rsphillips@chem.uga.edu
Robert S
RS
Phillips
Edith W
EW
Miles
Peter
P
McPhie
Stephane
S
Marchal
Reinhard
R
Lange
Georg
G
Holtermann
Roger S
RS
Goody
D000494:Allosteric Regulation; D002412:Cations; D006874:Hydrostatic Pressure; D007700:Kinetics; D008024:Ligands; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D020836:Protein Structure, Quaternary; D021122:Protein Subunits; D012486:Salmonella typhimurium / Q000201:enzymology* / Q000235:genetics; D012694:Serine / Q000737:chemistry; D012997:Solvents; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D013816:Thermodynamics; D014367:Tryptophan Synthase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D002412:Cations; D008024:Ligands; D021122:Protein Subunits; D012997:Solvents; D012694:Serine; D014367:Tryptophan Synthase