Evolutionary Origin of the P2X7 C-ter Region: Capture of an Ancient Ballast Domain by a P2X4-Like Gene in Ancient Jawed Vertebrates

Abstract

P2X purinergic receptors are extracellular ATP-gated ion channel receptors present on the cell plasma membrane. P2X receptors have been found in Metazoa, fungi, amoebas, and in plants. In mammals, P2X7 is expressed by a large number of cell types and is involved in inflammation and immunity. Remarkably, P2X7 does not desensitize as other P2X do, a feature linked to a "C-cysteine anchor" intra-cytoplasmic motif encoded by exon 11. Another specific feature of P2X7 is its C-terminal cytoplasmic ballast domain (exon 13) which contains a zinc (Zn) coordinating cysteine motif and a GDP-binding region. To determine the origin of P2X7, we analyzed and compared sequences and protein motifs of the C-terminal intra-cytoplasmic region across all main groups of Metazoa. We identified proteins with typical ballast domains, sharing a remarkably conserved Zn-coordinating cysteine motif. Apart from vertebrates, these ballast domains were not associated with a typical P2X architecture. These results strongly suggest that P2X7 resulted from the fusion of a P2X gene, highly similar to P2X4, with an exon encoding a ballast domain. Our work brings new evidence on the origin of the P2X7 purinergic receptor and identifies the Zn-coordinating cysteine domain as the fundamental feature of the ancient ballast fold.

P2X7 in Cancer: From Molecular Mechanisms to Therapeutics

“…Both genes are believed to be derived from successive gene duplications (Dubyak, 2007;Hou and Cao, 2016). Indeed, a recent report suggests that P2X7 was probably formed in lower vertebrates through the fusion of a P2X4-like gene with a Zn-coordinating cysteine-based domain (ZCD) coding exon (Rump et al, 2020). While heteromerisation of P2X7 and P2X4 in vivo is still controversial, both genes are found to be widely coexpressed (Guo et al, 2007;Kaczmarek-Hajek et al, 2012) and colocalize to act in concert in the regulation of the same physio-pathological functions (Kopp et al, 2019).…”

P2X7 Variants in Oncogenesis

“…The authors reported the presence of a C-cys anchor domain that, if palmitoylated, causes the typical non-desensitizing current associated with P2X7. Based on this molecular structure, a following study proposed that the P2X7 C terminal domain was acquired by genomic rearrangement from a P2X4-like gene in ancient jawed vertebrates generating the actual mammalian P2X7 [ 17 ]. Therefore, it is not completely surprising that some P2X7 splice variants, which function as a channel but not as macropore have been conserved through evolution [ 18 ].…”

Differential sensitivity of acute myeloid leukemia cells to daunorubicin depends on P2X7A versus P2X7B receptor expression

“…P2X7R activated macropore opening was also shown to enhance the intracellular uptake of drugs including chemotherapeutics such as doxorubicin 17 and was therefore proposed as tumor cell-specific drug delivery system 18,19 . The structure of P2X7R C terminal was recently reported 20 and it was speculated that this region was acquired by genomic rearrangement from a P2X4R like-gene in ancient jawed vertebrates generating the actual mammalian P2X7R 21 . It is therefore not surprising that certain species such as humans still express functional P2X7R splice variants missing the C terminal domain such as P2X7RB, an isoform unable to form the macropore, and thus without cytotoxic activity, but still endowed with ion channel properties 22,23 .…”