Eukaryotic Cell-Cell Fusion Families

The capacity of cells to unite in a regulated fashion, through fusion of their plasma membranes, is essential for reproduction and development in eukaryotes. Yet, the majority of proteins that mediate this process (i.e. fusogens) remain unidentified or uncharacterized. The Fusion Family (FF) and the Syncytins are the first families of cell-cell fusogens. The FF fusion proteins are required in both fusing cell membranes and their structure reveals the formation of flower-like super-complexes. The Syncytins were recently acquired from retroviruses and are similar to the Env glycoprotein of HIV. While there are apparent similarities between these families, their mechanisms are different. These similar and disparate principles may be relevant to other cell fusion events. Thus, FF proteins and Syncytins serve as paradigms for the mechanisms of eukaryotic cell fusion and provide insight to the ongoing quest for the missing fusogens.