Solution X-ray scattering studies of the yeast phosphofructokinase allosteric transition. Characterization of an ATP-induced conformation distinct in quaternary structure from the R and T states of the enzyme.

ABSTRACT

The allosteric transition of yeast phosphofructokinase has been studied by solution x-ray scattering. The scattering curves corresponding to the native enzyme (T conformation) were found to be similar to the curves recorded in the presence of saturating concentrations of fructose 6-phosphate (R conformation) or AMP (R or R' conformation). However, the curves obtained in the presence of ATP are clearly different the radius of gyration increases and the secondary minima and maxima are systematically shifted to lower angles, suggesting a swelling of the enzyme in the presence of ATP. These results give the first direct evidence for the existence of an ATP-induced T' conformation, distinct in quaternary structure from the R and T states of the enzyme oligomer, in agreement with our previous modeling of yeast phosphofructokinase regulation. X-ray scattering data are discussed in relation to the distinct molecular mechanisms of the ATP and fructose 6-phosphate allosteric effects involving, respectively, sequential and concerted conformational changes of the enzyme oligomer.