Journal Club: Structural analysis of P2X2 receptors show 2 different desensitization confirmations

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Today's journal article

Westermann FG, Oken AC, Granith PKE, Marimuthu P, Müller CE, Mansoor SE. Subtype-specific structural features of the hearing loss-associated human P2X2 receptor. 

Why I picked this article

The P2X2 receptor (P2X2R) is known to play a critical role in cochlear function. P2X2R is an ATP-gated ion channel with slow desensitisation, found in various cells, including sensory cells in the cochlea. Mutations in P2X2R are linked to age-related and noise-induced hearing loss in humans. Understanding how this receptor works at a molecular level is essential for targeting it therapeutically, but up until now, we didn’t have high-resolution structural information of the P2X2 protein. 

This study used cryo-electron microscopy (cryo-EM) to reveal detailed 3D structures of the human P2X2R, which might guide drug development for hearing loss.

Some of the research findings

Figure 5 B&C. Watermann et al. (2025)

Model:

  • Wild type human P2X2 gene was put into an expression "vector" (carrier molecule based on viral dna), to produce P2X2 receptors in cells. 
  • P2X2 gene was modified so that P2X2 protein will be tagged with green fluorescent protein. 
  • After HEK cells were producing P2X2, P2X2 proteins were purified and analysed. 
  • Cryoelectron microscopy was used to visualise P2X2 proteins in both desensitised state (without ATP) and in sensitised state (after being exposed to ATP). 

Finding:

  • ATP-bound desensitised states showed how ATP interacts with the receptor — the binding is subtype-specific and involves free anionic ATP forming tight interactions at the orthosteric site. (head to tables 1 & 2 for comparison across P2X members!)

  • Discovered two desensitised states (head to Figure 5 for the summary):

    • One matched previous models seen in other P2X receptor subtypes, and the second was a novel state; featuring significant movement in a loop adjacent to the binding site.

    • Molecular dynamics simulations supported these conformational shifts and proposed a path for ATP entry/exit into the binding site.

    • This loop may play a central role in activation/desensitisation dynamics, making it a potential drug target.

Haruna's takeaway

This is very exciting publication!! We are absolutely interested in this work, as we have an interest in purinergic signalling, which includes P2X2 receptors. P2X2 receptor is one type of protein out of a protein family called P2X receptors, which has seven members in the family in mammals (P2X1-7). The problem is that P2X receptor family members are very similar, and there are not many drugs that are "specific" to a particular P2X receptor. A detailed understanding of the P2X2 structure could lead to new compounds that can specifically activate or inhibit P2X2 receptors, without activating other members of the P2X, allowing the development of targeted therapies focusing on the P2X2.  

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This is Haruna's 40/100 of the 100-day challenge to post a science blog article every day! I love inner ear biology & cochlear physiology.