CASTOR family members are well-conserved in eukaryotes (including human, chimpanzee, dog, cow, mouse, rat, chicken, zebrafish) [, ]. Three subtypes, designated CASTOR1, CASTOR2 and CASTOR3, have been identified in humans.CASTOR1 can form homodimers and bind arginine. It can also form heterodimers with CASTOR2 []. The arginine binding of CASTOR1 disrupts the CASTOR1-GATOR2 interaction, and this triggers downstream activation of mTORC1 []. Therefore, CASTOR1 functions as an intracellular arginine sensor for the mTORC1 Pathway [, ]. Interestingly, CASTOR1 shares substantial structural homology with the lysine-binding regulatory domain of prokaryotic aspartate kinases [].
