Roles of ALG-2 and its interacting protein in apoptosis and signal transduction

ALG-2 is a new 22 kDa intracellular calcium-binding protein involved in apoptosis. Forced reduction of ALG-2 gene expression makes the antisense-DNA-transfected T cell-lines resistant to apoptosis induced by various stimuli. ALG-2 belongs to the penta-EF-hand protein family which includes the calpain small subunit, sorcin, grancalcin and peflin in mammals. The family members contain five EF-hand motifs in their C-termini. The N-terminal regions are rich in glycine and hydrophobic residues. ALG-2 binds to a newly identified protein named Alix or AIP1. The overall structure of Alix/AIP1 is similar to Xenopus oocyte phosphoprotein Xp95, Aspergillus nidulans alkaline adaptation factor PalA and the budding yeast protein named BRO1 involved in a MAP kinase cascade. A similar sequence is also found in a hypothetical protein of plant. All these proteins contain a potential tyrosine-phosphorylation site and a few PXXP motifs (SH3-binding sites), suggesting involvement of ALG-2 or its homologs in basic signal transduction common in all eukaryotic cells.