UDP-Galactose 4′-Epimerase Activities toward UDP-Gal and UDP-GalNAc Play Different Roles in the Development of Drosophila melanogaster

Abstract

In both humans and Drosophila melanogaster, UDP-galactose 4′-epimerase (GALE) catalyzes two distinct reactions, interconverting UDP-galactose (UDP-gal) and UDP-glucose (UDP-glc) in the final step of the Leloir pathway of galactose metabolism, and also interconverting UDP-N-acetylgalactosamine (UDP-galNAc) and UDP-N-acetylglucosamine (UDP-glcNAc). All four of these UDP-sugars serve as vital substrates for glycosylation in metazoans. Partial loss of GALE in humans results in the spectrum disorder epimerase deficiency galactosemia; partial loss of GALE in Drosophila melanogaster also results in galactose-sensitivity, and complete loss in Drosophila is embryonic lethal. However, whether these outcomes in both humans and flies result from loss of one GALE activity, the other, or both has remained unknown. To address this question, we uncoupled the two activities in a Drosophila model, effectively replacing the endogenous dGALE with prokaryotic transgenes, one of which (Escherichia coli GALE) efficiently interconverts only UDP-gal/UDP-glc, and the other of which (Plesiomonas shigelloides wbgU) efficiently interconverts only UDP-galNAc/UDP-glcNAc. Our results demonstrate that both UDP-gal and UDP-galNAc activities of dGALE are required for Drosophila survival, although distinct roles for each activity can be seen in specific windows of developmental time or in response to a galactose challenge. By extension, these data also suggest that both activities might play distinct and essential roles in humans.

UDP-hexose 4-epimerases: a view on structure, mechanism and substrate specificity

“…11 It has also been found that UDP-galactose 4-epimerase plays an essential role in development and homeostasis of Drosophila that extends beyond the Leloir pathway. 12 On the other hand, UDP-sugars are also important as precursors in lipopolysaccharides (LPS). LPS is involved in several aspects of cell-cell interactions, such as host-pathogen interactions 13 and biofilm formation.…”

Tailoring recombinant protein quality by rational media design

“…In contrast, more abundant intracellular UDP-glucose coincided with higher galactosylation. The enzyme UDP-galactose 4'-epimerase interconverts UDP-glucose and UDP-galactose in the final step of the Leloir pathway of galactose metabolism, while galactose-1-phosphate uridyl transferase is involved in the second step of the pathway, catalyzing the transformation of UDP-glucose and galactose-1-phosphate to glucose-1-phosphate and UDP-galactose 124,302 . In comparison to other process formats, in process A the substrate demand of galactosyltransferase was lower after day 6.…”

Drosophila melanogaster Models of Galactosemia

“…al. [32], Daenzer and colleagues [7] created a time course series of Drosophila that experienced dGALE knockdown with concurrent induction of either hGALE, eGALE, wbgU , or both eGALE and wbgU at successive stages of development. As expected, RNAi knockdown of dGALE during both embryonic and larval stages of development was lethal, but was rescued by expression of either hGALE or eGALE + wbgU .…”