TTR-52 was called family 2 in [1], and has weak similarity to transthyretin (formerly called pre-albumin) which transports thyroid hormones. The specific function of this protein is as a bridging molecule in apoptosis cross-linking dying cells to phagocytes. TTR-52 bridges by cross-linking surface-exposed phosphatidylserine (PtdSer) on apoptotic cells to the CED-1 receptor, a transmembrane receptor, on phagocytes. TTR-52 has an open beta-barrel-like structure [2].

1: Analysis of protein domain families in Caenorhabditis elegans. Sonnhammer EL, Durbin R; Genomics 1997;46:200-216. PMID:9417907

2: Structural study of TTR-52 reveals the mechanism by which a bridging molecule mediates apoptotic cell engulfment. Kang Y, Zhao D, Liang H, Liu B, Zhang Y, Liu Q, Wang X, Liu Y; Genes Dev. 2012;26:1339-1350. PMID:22713871