2019 Volume 88 Issue 3 Pages 3_055-3_064
Fructose 1, 6-bisphosphate aldolase (EC 4.1. 2.13.; ALD) is a key enzyme in cellular carbon–carbon bond formation or breakage, and plays roles in both glycolysis and gluconeogenesis in the cytoplasm of higher organisms. Here we report the identification, expression analysis and functional characterization of ALD genes from the silkworm, Bombyx mori. In contrast to the single gene in Drosophila melanogaster, the lepidopteran silkworm genome was found to possess two ALD genes, BmALD1 and BmALD2. The phylogenetic tree of the arthropod ALD clearly showed that insect ALDs can be classified into two classes, the typical ALDs present in various insect species (group I; including BmALD1) and the lepidopteran-specific ALDs (group II; including BmALD2). Among the eight larval organs examined, BmALD1 mRNA showed the highest expression in muscle, followed by the head, and BmALD2 was widely expressed except in the head and mid-gut; the highest expression was observed in muscle. The homo-tetramer enzymes of BmALD1 and BmALD2 were expressed as recombinant proteins in Escherichia coli (rBmALD1 and rBmALD2, respectively), from which they were purified to homogeneity. Two types of ALD could be distinguished by the activity ratio towards the two substrates fructose 1, 6-bisphosphate (FBP)/fructose 1-phosphate (F1P) and the effect of pH on the activities, and these properties of rBmALD1 resembled those of Drosophila ALD. The results of this study show the indispensable role of B. mori ALDs in the control of tissue-specific sugar-phosphate metabolisms, and will provide a basis for studying the evolution of insect ALD genes.
