The BH4 domain of Bcl-2 orthologues from different classes of vertebrates can act as an evolutionary conserved inhibitor of IP receptor channels.

Ca signalling plays an important role in various physiological processes in vertebrates. In mammals, the highly conserved anti-apoptotic B-cell lymphoma-2 (Bcl-2) protein is an important modulator of the inositol 1,4,5-trisphosphate receptor (IPR), i.e. the main intracellular Ca - release channel located at the endoplasmic reticulum (ER). The Bcl-2 Homology (BH) 4 domain of Bcl-2 (BH4-Bcl-2) is a critical determinant for inhibiting IPRs, by directly targeting a region in the modulatory domain of the receptor (domain 3). In this paper, we aimed to track the evolutionary history of IPR regulation by the BH4 domain of Bcl-2 orthologues from different classes of vertebrates, including Osteichthyes, Amphibia, Reptilia, Aves and Mammalia. The high degree of conservation of the BH4 sequences correlated with the ability of all tested peptides to bind to the domain 3 of mouse IPR1 in GST-pull downs and their overall ability to inhibit IP-induced Ca release (IICR) in permeabilized cells. Nevertheless, the BH4 domains differed in their potency to suppress IICR. The peptide derived from X. laevis was the least potent inhibitor. We identified a critical residue in BH4-Bcl-2 from H. sapiens, Thr7, which is replaced by Gly7 in X. laevis. Compared to the wild type X. laevis BH4-Bcl-2, a "humanized" version of the peptide (BH4-Bcl-2 Gly7Thr), displayed increased IPR-inhibitory properties. Despite the differences in the inhibitory efficiency, our data indicate that the BH4 domain of Bcl-2 orthologues from different classes of vertebrates can act as a binding partner and inhibitor of IPR channels.