Calponin-Like Chd64 Is Partly Disordered

20-hydroxyecdysone (20E) and juvenile hormone (JH) signaling pathways interact to regulate insect development. Recently, two proteins, a calponin-like Chd64 and immunophilin FKBP39 have been found to play a pivotal role in the cross-talk between 20E and JH, although the molecular basis of interaction remains unknown. The aim of this work was to identify the structural features that would provide understanding of the role of Chd64 in multiple and dynamic complex that cross-links the signaling pathways. Here, we demonstrate the results of in silico and in vitro analyses of the structural organization of Chd64 from Drosophila melanogaster and its homologue from Tribolium castaneum. Computational analysis predicted the existence of disordered regions on the termini of both proteins, while the central region appeared to be globular, probably corresponding to the calponin homology (CH) domain. In vitro analyses of the hydrodynamic properties of the proteins from analytical size-exclusion chromatography and analytical ultracentrifugation revealed that DmChd64 and TcChd64 had an asymmetrical, elongated shape, which was further confirmed by small angle X-ray scattering (SAXS). The Kratky plot indicated disorderness in both Chd64 proteins, which could possibly be on the protein termini and which would give rise to specific hydrodynamic properties. Disordered tails are often involved in diverse interactions. Therefore, it is highly possible that there are intrinsically disordered regions (IDRs) on both termini of the Chd64 proteins that serve as platforms for multiple interaction with various partners and constitute the foundation for their regulatory function.