Interaction patterns of methoprene-tolerant and germ cell-expressed Drosophila JH receptors suggest significant differences in their functioning

Methoprene-tolerant (Met) and germ cell-expressed (Gce) proteins were shown to be juvenile hormone (JH) receptors of Drosophila melanogaster with partially redundant functions. We raised the question of where the functional differentiation of paralogs comes from. Therefore, we tested Met and Gce interaction patterns with selected partners. In this study, we showed the ability of Gce and its C-terminus (GceC) to interact with 14-3-3 in the absence of JH. In contrast, Met or Met C-terminus (MetC) interactions with 14-3-3 were not observed. We also performed a detailed structural analysis of Met/Gce interactions with the nuclear receptor fushi tarazu factor-1 (Ftz-F1) ligand-binding domain. We showed that GceC comprising an Ftz-F1-binding site and full-length protein interacts with Ftz-F1. In contrast to Gce, only MetC (not full-length Met) can interact with Ftz-F1 in the absence of JH. We propose that the described differences result from the distinct tertiary structure and accessibility of binding sites in the full-length Met/Gce. Moreover, we hypothesize that each interacting partner can force disordered MetC and GceC to change the structure in a partner-specific manner. The observed interactions seem to determine the subcellular localization of Met/Gce by forcing their translocation between the nucleus and the cytoplasm, which may affect the activity of the proteins. The presented differences between Met and Gce can be crucial for their functional differentiation during D. melanogaster development and indicate Gce as a more universal and more active paralog. It is consistent with the theory indicating gce as an ancestor gene.