Gene structure, evolutionary analysis and transport activity of the D. melanogaster mitochondrial glutamate/aspartate carrier

In mammals, the mitochondrial aspartate/glutamate carrier (AGC) is involved in cell REDOX homeostasis, as it’s a component of the malate-aspartate shuttle allowing cytosolic NADH import into the mitochondrial matrix to promote oxidative phosphorilation. AGC takes also part in many metabolic pathways, i.e. urea cycle, gluconeogenesis from lactate and neuron myelin biosynthesis. In man, two tissue-specific isoforms, AGC1 and AGC2 (called aralar and citrin) encoded by two different genes, were identified and characterized [1]. In order to fill the existing gap of knowledge in an important model organism such as D. melanogaster, we studied aralar1 gene, which is orthologous of human AGC-encoding genes, showing that three out of the six known transcriptional isoforms are constitutively expressed, whereas three of them display a biased expression pattern in tissues or through development. The observed expression profile could be related to the presence of two functional elements identified within an intron. The comparative analysis performed on the exon/intron structure of orthologous genes suggests that a single glutamate/aspartate carrier gene was present in the genome of the common ancestor of Arthropoda. Recombinant proteins Aralar1-PA and Aralar1-PE, reconstituted into liposomes, share the same efficiency to exchange glutamate against aspartate and the same substrate affinities with human isoforms. Although the two fruit fly isoforms diverge only in their calcium-binding domain, Aralar1-PA and Aralar1-PE greatly differ in their specific activities and substrate specificity, identifying them as the human aralar and citrin counterparts, respectively. The tight regulation of aralar1 transcripts’ expression and the high request of aspartate and glutamate during early embryogenesis suggest a crucial role of Aralar1 in this developmental stage.