Large-scale filament formation inhibits the activity of CTP synthetase.
Bottom Line: Structure-guided mutagenesis and mathematical modeling further indicate that coupling activity to polymerization promotes cooperative catalytic regulation.This previously uncharacterized regulatory mechanism is important for cellular function since a mutant that disrupts CtpS polymerization disrupts E. coli growth and metabolic regulation without reducing CTP levels.We propose that regulation by large-scale polymerization enables ultrasensitive control of enzymatic activity while storing an enzyme subpopulation in a conformationally restricted form that is readily activatable.
Affiliation: Department of Molecular Biology, Princeton University, Princeton, United States.Show MeSH
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Mentions: We compared the sharpness of enzyme inhibition in our novel polymerization-based mechanism to that of previously characterized mechanisms of enzyme inhibition such as competitive and allosteric inhibition (Figure 8D; Supplementary file 1). We found that, among the mechanisms examined, the ones involving polymerization-based negative feedback yield the sharpest decrease in enzyme activity when CTP levels are increased, thereby enabling tight regulation of CTP production by CTP levels. Our estimate based on average CtpS filament length of the value of the nucleation energy yields extremely sharp transitions (see Figure 8D, where this estimate was used, and our discussion of response coefficients in Supplementary file 1). This sharpness is apparent in comparing the concentration dependences of CtpS specific activity in the presence of CTP. The CTPS0.5 value at 400 μM CTP is slightly shifted compared to no CTP. At 800 μM, the CtpS0.5 value is substantially decreased and the curvature more concave (Figure 8—figure supplement 3).
Affiliation: Department of Molecular Biology, Princeton University, Princeton, United States.