A new perspective on the evolution of the interaction between the Vg/VGLL1-3 proteins and the TEAD transcription factors

Abstract

The most downstream elements of the Hippo pathway, the TEAD transcription factors, are regulated by several cofactors, such as Vg/VGLL1-3. Earlier findings on human VGLL1 and here on human VGLL3 show that these proteins interact with TEAD via a conserved amino acid motif called the TONDU domain. Surprisingly, our studies reveal that the TEAD-binding domain of Drosophila Vg and of human VGLL2 is more complex and contains an additional structural element, an Ω-loop, that contributes to TEAD binding and in vivo function. To explain this unexpected structural difference between proteins from the same family, we propose that, after the genome-wide duplications at the origin of vertebrates, the Ω-loop present in an ancestral VGLL gene has been lost in some VGLL variants. These findings illustrate how structural and functional constraints can guide the evolution of transcriptional cofactors to preserve their ability to compete with other cofactors for binding to transcription factors. elucidation of the structures of the YAP:TEAD (Chen, Chan et al., 2010, Li, Zhao et al., 2010 and of the VGLL1:TEAD (Pobbati, Chan et al., 2012) complexes has shed some light on how these proteins bind to TEAD. The TEAD-binding domain of YAP is formed of a β-strand:αhelix:Ω-loop motif while the TEAD-binding domain of VGLL1 contains only a β-strand:αhelix motif, known as TONDU domain, which binds to TEAD in a fashion similar to the βstrand:α-helix region of YAP ( Fig S1) (Li et al., 2010). The residues present in the TONDU domain of VGLL1 are well-conserved amongst the members of the Vg/VGLL1-3 family (Vg, vestigial, Drosophila homolog of VGLL1-3) (Simon, Faucheux et al., 2016) and no other regions of these proteins outside this motif have so far been reported to play a direct role in the interaction with TEAD proteins. Therefore, the main structural difference between the TEADbinding domain of these two cofactor families is the presence of an Ω-loop in the Yki/YAP proteins (Yki, Yorkie, Drosophila homolog of YAP), but not in the Vg/VGLL1-3 proteins.However, we made an observation which suggests that some members of the Vg/VGLL1-3 family may also possess an Ω-loop in their TEAD-binding domain. We identified a region in the amino acid sequence of the Vg protein from Drosophila melanogaster, residues 323-334 (Vg 323-334 ), which has a strong homology with the Ω-loop of YAP and is separated from the TONDU domain (Vg 288-311 ) by a similar number of residues compared with the Ω-loop from the β-strand:α-helix region in YAP ( Fig 1A). This unexpected finding, which suggests that Vg contains an Ω-loop, echoes earlier findings. Simmonds et al. have mapped the Sd-binding domain of Vg (Sd, Scalloped, Drosophila homolog of human TEAD) to Vg 279-335 , which contains not only the TONDU domain but also the putative Ω-loop, Vg 323-334 (Simmonds, Liu et al., 1998). However, these authors did not conduct experiments with shorter fragments to determine whether the entire Vg 279-335 is required for efficient binding to Sd. In their study of the ladybird beetl...