This family consists of apoptosis inhibitory protein 5 (API5) sequences from several organisms. Apoptosis or programmed cell death is a physiological form of cell death that occurs in embryonic development and organ formation. It is characterised by biochemical and morphological changes such as DNA fragmentation and cell volume shrinkage. API5 is an anti apoptosis gene located in Homo sapiens chromosome 11, whose expression prevents the programmed cell death that occurs upon the deprivation of growth factors [, ]and is up-regulated in various cancer cells. This protein has an elongated all α-helical structure, in which the N-terminal half is similar to the HEAT repeat and the C-terminal half is similar to the ARM (Armadillo-like) repeat. This suggests that API5 is involved in protein-protein interactions and may act as a scaffold for multiprotein complexes [].
