Identification of the Calcium Binding Sites in Translationally Controlled Tumor Protein

Translationally controlled tumor protein (TCTP), also known as IgE-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 and ⁴⁵Ca²⁺-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.