Title: Structure Prediction and Sequence Phylogeny of Fusion Family (FF) Proteins Indicate a Common Ancestor in Nematodes and Horizontal Gene Transfer Origin in Non-Nematodes13
The fusexin superfamily comprises proteins that mediate cell-cell fusion during viral infections, somatic development and sexual reproduction, and have also been identified in Archaea. Among them, a subfamily of FF proteins, first identified in the nematode C. elegans, exhibits a striking structural similarity to Class II viral fusogens. This similarity, however, is absent at the sequence level, making their evolutionary origin difficult to pinpoint. By analyzing the phylogenetic relationships and structural predictions of FF candidate ectodomains, we present a phylogenetic inquiry of FF proteins in both nematode and non-nematode species. Results show that nematodes harbor two distinct FF subgroups, which correspond to the C. elegans fusogens EFF-1 and AFF-1 and align with nematode phylogeny. In contrast, the general phylogeny of FF in non-nematode species diverges from broader invertebrate evolution. The results reveal the variable origins of FF proteins and suggest divergence in their structural properties as well
