Researchers at Weill Cornell Medicine mapped how the signaling lipid PIP2 blocks human rod cyclic nucleotide-gated ion channels, according to a study published in Nature Communications. The mechanism demonstrates how phosphatidylinositol-4,5-bisphosphate, or PIP2, halts channel activation by binding to an allosteric site on CNGA1, the principal subunit of rod cyclic nucleotide-gated (CNG) channels.
Earlier reports of low PIP2 concentrations in rod outer segment membranes had cast doubt on whether lipid inhibition played a functional role in vision, leaving the inhibition mechanism unexplained. Using purified, liposome-reconstituted CNGA1 channels, researchers Taehyun Park and Crina M. Nimigean ran flux assays and single-channel electrophysiology. These tests demonstrated that PIP2 inhibits channel activity at the lower concentrations estimated to occur naturally in rod outer segment membranes, confirming the physiological relevance of the process.
Cryogenic electron microscopy structures revealed how the lipid halts channel function at the molecular level. When researchers observed PIP2-free channels reconstituted into lipid nanodiscs, cryo-EM imaging captured closed, intermediate, and open conformations. In contrast, channels prepared with PIP2 showed no open conformation. The imaging showed that PIP2 binds directly at the structural interface between the voltage-sensing, pore, and C-linker domains. This binding stabilizes closed channel states and sterically blocks the channel from opening, identifying an inhibitory allosteric site that could serve as a target for therapeutic compounds.
The cryo-EM data were collected at facilities operated by Weill Cornell Medicine and NYU Langone, with screening and data collection support from Edwin C. Fluck, Bing Wang, Huihui Kuang, and Bill Rice. Youxing Jiang of the University of Texas Southwestern Medical Center provided the pEZT-BM-CNGA1 plasmid used to produce CNGA1-expressing baculovirus. The National Institutes of Health funded the work through grant GM124451 awarded to Nimigean, while Park declared no relevant funding.
