Figure 6: Predicted Pre-metazoan Proteins Include Several YxxP Motifs.

The diagrams illustrate two groups of predicted/uncharacterized proteins: 1) three S. rosetta proteins identified by BLASTP with the Bcar1 and Dok7 peptide sequences that bind to the M. brevicollis crka1 SH2 domain (Table 1; Supplementary Table S5 and 2) two M. brevicollis proteins identified by a profile hidden Markov model constructed from the metazoan bcar1 alignment shown in Supplementary Figure S10a without the SH3 domain. Despite the fact that they are identified by two independent methods, all 5 proteins are transmembrane proteins with several YxxP motifs in the predicted cytosolic region. Closed boxes across the membrane indicate predicted transmembrane regions. PTSG_05573 has an extracellular DUF5011 domain that has not been assigned to known functions. PTSG_12435 and 12436 have a C2 domain (Ca²⁺-dependent phospholipid binding domain) after the N-terminal signal peptide. In PTSG_12436, repeats of EGF-like domains likely mediate protein-protein interactions. In M. brevicollis A9VAL3, the extracellular region includes three thrombospondin type 1 repeats (TSP1) that may mediate cell-cell interactions or ligand-receptor binding. In M. brevicollis A9V449, the extracellular region includes a cysteine-rich growth factor receptor (GFR) domain found frequently in mammalian growth factor receptors such as EGFR, PDGFR and IGF1R, as well as a DUF domain. PTSG_05573, A9VAL3, and A9V449 have SH2-like domains (SH2SF: SH2 domain superfamily) near the C-terminus. A9VAL3 and A9V449 are UniProt accession numbers, while PTSG_05573, 12435 and 12436 are current gene symbols/IDs.