Identification of the calcium binding sites in translationally controlled tumor protein

Translationally controlled tumor protein (TCTP), also known as lgE-dependent histamine-releasing factor, is a growth-related tumor protein. Although the primary sequence of rat TCTP does not reveal any recognizable Ca2+-binding motif, previous studies have demonstrated that rat TCTP consisting of 172 amino acids is a Ca2+-binding protein. However, the region of TCTP required for Ca2+ interaction has not been mapped to the molecule. Here, we reported that the Ca2+ binding region of TCTP, which was mapped by using a combination of deletion constructs of rat TCTP and45Ca2+-overlay assay, was confined to amino acid residues 81–112. This binding domain did not show any peculiar loop of calcium-binding motif such as CaLB domain and EF hand motif and it seems to be constituted of random coil regions neighboring the a helix. Thus, our data confirm that TCTP is a novel family of Ca2+-binding protein.