Structural change of the enterobactin synthetase in crowded solution and its relation to crowding-enhanced product specificity in nonribosomal enterobactin biosynthesis.

Significant conformational change is detected by circular dichroism and fluorimetry for the major component of the enterobactin synthetase in crowded solutions mimicking the intracellular environment. The structural change correlates well with the extent of the crowding-induced side product suppression in nonribosomal enterobactin synthesis. In contrast, protein-stabilizing solvophobic agents such as glycerol have no effect on the formation of side products, excluding crowding-induced protein stability as a cause for the observed enhancement of the product specificity of the synthetase. These results strongly support that macromolecular crowding is an indispensable physiological factor for normal functioning of the nonribosomal enterobactin synthetase by altering the active sites to increase its product specificity.