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 human chromosome 11, whose expression prevents the programmed cell death that occurs upon the deprivation of growth factors [1,2] and is up-regulated in various cancer cells. This protein has an elongated all alpha-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 [3].

1: Molecular cloning and fine mapping of API5L1, a novel human gene strongly related to an antiapoptotic gene. Gianfrancesco F, Esposito T, Ciccodicola A, D'Esposito M, Mazzarella R, D'Urso M, Forabosco A; Cytogenet Cell Genet 1999;84:164-166. PMID:10393420

2: AAC-11, a novel cDNA that inhibits apoptosis after growth factor withdrawal. Tewari M, Yu M, Ross B, Dean C, Giordano A, Rubin R; Cancer Res 1997;57:4063-4069. PMID:9307294

3: Helical repeat structure of apoptosis inhibitor 5 reveals protein-protein interaction modules. Han BG, Kim KH, Lee SJ, Jeong KC, Cho JW, Noh KH, Kim TW, Kim SJ, Yoon HJ, Suh SW, Lee S, Lee BI; J Biol Chem. 2012;287:10727-10737. PMID:22334682