Figure 2. The family of Trio proteins. The name of Trio refers to the fact that Trio displays three enzymatic domains, two GEF and one serine kinase domains. In addition, Trio harbors numerous accessory domains. Listed from N-terminus to C-terminus, these include: a CRAL-Trio/Sec14 motif, several spectrin-like repeats, two SH3 motifs and an Immunoglobulin (Ig) domain. The Trio family consists of two paralogs in mammals, Trio and Kalirin. Two orthologs of Trio/Kalirin exist in invertebrates, UNC-73 in C. elegans and D-Trio in D. melanogaster. The overall organization of Trio family proteins in different organisms is remarkably conserved. The main divergence between the proteins occurs after the second GEF domain, where only vertebrate Trio and Kalirin proteins harbor a serine kinase domain. The percentage of identity at the protein level between Trio and the other members is shown.