Calcium ions are utilised as a second messenger in all forms of cellular life. In contrast to bacteria and archaea, eukaryotes possess endomembrane systems, exemplified by the endoplasmic reticulum. Such organelles act as intracellular stores in Ca2+ signalling processes, with two distantly related calcium channels, the inositol 1,4,5- trisphosphate receptors and ryanodine receptors, acting as Ca2+ release mechanisms. Despite their fundamental role, the evolutionary origins of such Ca2+ release channels have proven difficult to elucidate. The current study presents updates on the phylogeny of this channel superfamily and analyses of the domain architectures of these proteins.
One key difference in the cell biology of eukaryotes compared to bacteria and archaea is the presence of endomembrane systems, including the endoplasmic reticulum (ER). Such endomembrane systems permit compartmentalisation of cellular activities and are endowed with unique subsets of proteins that perform these specialised roles. Many of these endomembrane located proteins lack detectable homologues in archaea and bacteria.