Molecular interaction of α-synuclein with p2x7 receptor

Introduction

Alpha-synuclein

Researchers have identified and sequenced two proteins in the human brain, consisting of 140 and 134 amino acids, respectively. These proteins, alpha-synuclein (140 amino acids) and beta-synuclein (134 amino acids), share 61% sequence identity. Both are predominantly expressed in the brain and are concentrated in presynaptic nerve terminals. The name "alphasynuclein" originates from its discovery on synaptic vesicles and nuclear envelopes isolated from the Torpedo electric organ [5] . The α-synuclein protein, encoded by the SNCA gene on the long arm of chromosome 4 (4q22.1), has a molecular weight of approximately 15 kDa [2] . Under normal physiological conditions, α-synuclein associates with synaptic vesicle membranes, facilitating neurotransmitter release via the SNARE complex. When α-synuclein becomes abnormal or forms toxic aggregates, this process is disrupted, leading to impaired vesicle clustering and inefficient SNARE complex assembly. Such disruptions can compromise neuronal communication and contribute to long-term neuronal damage and cell death [10] . The misfolding and aggregation of α-synuclein into amyloid fibrils are key features of several neurodegenerative disorders, collectively termed synucleinopathies [8,20] . Its aggregation propensity is further enhanced by post-translational modifications, including phosphorylation, ubiquitination, nitration, and truncation [3] . α-Synuclein is distributed across multiple cellular compartments, including the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and synaptic vesicles [22] .

Structure of α-Syn

Alpha-synuclein (α-Syn) is composed of three distinct domains. The N-terminal domain (residues 1-60) is α-helical in structure and exhibits membrane-binding properties. The nonamyloid-β component (NAC) domain (residues 61-95) is highly prone to aggregation, forming amyloid fibrils and protofibrils. The C-terminal domain (residues 96-140) is rich in anionic residues [9] . Structurally, α-Syn can exist as an intrinsically disordered protein, adopt helical conformations, or display a combination of both [16] .

The N-terminal region contains several amphipathic 11residue repeats, including the KTKEGV consensus sequence, which is a hotspot for familial mutations [4] .

Alterations in α-Syn structure and function lead to its extracellular accumulation and fibril formation, ultimately causing damage to surrounding cells [11] .

P2RX7

De Salis et al. (2022), report that P2X receptors are classified into seven subtypes, P2X1 through P2X7, each encoded by distinct genes. Among these, the P2X7 receptor (P2X7R), encoded by the P2RX7 gene, is notable for its unique structure and functional properties [6] . Structurally, P2X7R is a trimeric receptor that functions as a nonselective cation channel activated by elevated extracellular ATP levels. Prolonged stimulation of P2X7R can lead to the formation of a large membrane pore, promoting cell death and increased ATP release into the extracellular environment [1] . This receptor allows the passage of small cations such as Ca²⁺, Na⁺, and K⁺, and in certain cell types, it can also transport larger positively charged molecules up to 900 Da in size [7] . P2X7R is widely expressed throughout the central nervous system and is implicated in the pathophysiology of several neurodegenerative and psychiatric disorders [7] . The human P2RX7 gene is located on chromosome 12q24.31, while in mice it is found on chromosome 5; it comprises 13 exons and encodes a 595-amino acid subunit. Before 2019, structural models of P2X7R were primarily based on X-ray crystallography, which, however, had limitations in accurately resolving the receptor's intracellular domains [13] .

Structure

In 2019, McCarthy and colleagues used cryogenic electron microscopy to elucidate the full structure of the rat P2RX7 receptor for the first time. Each P2RX7 subunit possesses intracellular N-terminal and C-terminal regions, two hydrophobic transmembrane domains, and a large extracellular loop that contains the ATP-binding site [6,28] . Structurally, the P2X7 receptor subunit has a dolphin-like appearance, with the extracellular domain forming the head and fins and the two transmembrane helices (TM1 and TM2) forming the tail [15] . Robinson et al. (2014), observed that P2X7 receptors situated in cholesterol-rich lipid rafts are regulated in their pore-forming capacity by the membrane's cholesterol content. Lipid rafts, characterized by high levels of cholesterol and sphingolipids, provide a supportive environment for receptor function. Elevating cellular cholesterol inhibits pore formation, whereas acute cholesterol depletion using methyl-β-cyclodextrin (MCD) enhances pore formation in response to agonists [19] . Cholesterol may exert its inhibitory effect either by directly binding to the P2X7 receptor or by altering membrane properties, though the precise mechanism remains unclear [17] .

Alpha-Synuclein and P2RX7 interaction

Multiple studies have highlighted the pivotal role of the purinergic receptor P2RX7 in α-synuclein induced mitochondrial dysfunction and neuroinflammation. Wilkaniec et al. (2020), reported that α-synuclein interaction with P2RX7 impairs mitochondrial function, elevates oxidative stress, and activates cytokines and immune cells, thereby initiating inflammatory responses. Additionally, increased extracellular ATP has been shown to activate P2RX7 in tumor microenvironments, enhancing antitumor immunity and underscoring the receptor's broader immunomodulatory functions [26,12] . Singh et al. (2024), provided further mechanistic insight using integrated computational methods, including data curation, molecular docking, molecular dynamics (MD) simulations, and structural analyses. Their results demonstrated that the N-terminal domain of α-synuclein preferentially binds to the proximal region of P2RX7's transmembrane domain. Microsecond-scale MD simulations within a lipid bilayer revealed that this binding induces significant structural fluctuations in P2RX7, particularly in regions involved in pore dilation, receptor desensitization, and calcium transport. Additional analyses of structural networks, residue contacts, and solvent accessibility identified key amino acids mediating this interaction [21,14] . Supporting these findings, Wei et al. (2025), showed that αsynuclein binding to the P2X7R transmembrane domain triggers reduced complex I activity of mitochondria. Furthermore, P2X7R activation recruits pannexin-1, forming large membrane pores that amplify oxidative stress and cellular damage. Together, these studies establish P2X7R as a central mediator of α-synuclein driven mitochondrial dysfunction, oxidative stress, neuroinflammation, and neurodegeneration [25] .

Discussion

α-Synuclein (α-Syn) is an intrinsically disordered protein predominantly expressed in neural tissues, where it plays a vital role in synaptic vesicle remodeling and neurotransmission [18,24] . Alterations in its structure or function are closely associated with neurological disorders, including Parkinson's disease (PD) and Alzheimer's disease [8, 20] . P2RX7, an ATP-gated transmembrane ion channel, is activated during both acute and chronic inflammatory states [12] . Prolonged activation of P2RX7 can lead to receptor desensitization, pore overstretching, cell death, and exacerbated inflammation [6] . Recent evidence indicates that α-Syn directly interacts with P2RX7, activating the receptor and promoting pore dilation, which contributes to mitochondrial dysfunction [27,26] . Computational studies, including data curation, molecular docking, molecular dynamics (MD) simulations, and structural analyses, suggest that the N-terminal domain of α-Syn preferentially binds near the transmembrane region of P2RX7 [21,14] . Furthermore, Wei et al., (2025) demonstrated that this interaction induces excessive Ca²⁺ influx, mitochondrial depolarization, complex I impairment, and reactive oxygen species (ROS) generation. P2RX7 also recruits pannexin-1 to form large membrane pores, amplifying oxidative stress and cellular damage, highlighting its central role in α-Synmediated mitochondrial dysfunction, neuroinflammation, and neurodegeneration. Understanding the interaction between P2RX7 and α-synuclein could be helpful in developing therapeutic strategies for diseases like involving these proteins [14] .

References

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