Structural insights into the class I fructose 1,6-bisphosphate aldolase in Escherichia coli

Fructose 1,6-bisphosphate aldolase (FBPA) is involved in glycolysis by catalyzing the reversible conversion of fructose 1,6-bisphosphate (F1,6BP) into dihydroxyacetone phosphate and glyceraldehyde 3-phosphate. Two classes have been reported with class I present in eukaryotes and class II in prokaryotes. Owing to FBPA’s role in glycolysis, class I and class II FBPA inhibitors have been developed for the treatment of communicable and noncommunicable diseases, such as tuberculosis and cancer. Escherichia coli is one of few organisms to have been reported to possess both classes (Ec-FBPA-I and Ec-FBPA-II), and an understanding of the molecular features of the two classes within a single organism may be useful for the design of potent and selective FBPA inhibitors. Here, we report the structure of Ec-FBPA-I apo and in complex with the F1,6BP Schiff base intermediate to 2.6 and 2.7 Å-resolution, respectively. Structural analysis of Ec-FBPA-I revealed the classic TIM-barrel fold of this family of enzymes. Ec-FBPA-I formed a homodecamer in the asymmetric unit, with a positively charged active site at the center of each TIM-barrel. F1,6BP was shown to be stabilized by four basic residues, in contrast to the binding mechanism for Ec-FBPA-II which utilizes an ion for binding of phosphate1, and a single basic residue for phosphate6. A comparison with the previously reported class I aldolase from Thermoproteus tenax, highlighted sequence and structural conservation of several key catalytic residues. In addition, through iterative BLAST searches and primary sequence analysis, we illustrate that the class I FBPA in bacteria is more widespread than previously reported.