Endofin is a FYVE domain-containing protein that strongly resembles SARA, the Smad anchor for receptor activation that facilitates TGF-beta signalling. Endofin acts in a similar manner as SARA, it binds to BMP-specific R-Smads, it localizes in early endosomes and it facilitates their phosphorylation, thus promoting signal transduction by the BMP receptors. However, it should be noted that endofin has also been reported to bind to the Co-Smad, Smad4, and to the TGF-beta type receptor, thus enhancing TGF-beta signalling. Since Smad4 is a common Smad that operates in the BMP-specific pathways, the latter observation might imply that endofin could regulate both TGF-beta and BMP signalling, a hypothesis still open for investigation.