CNGA3 achromatopsia-associated mutation potentiates the phosphoinositide sensitivity of cone photoreceptor CNG channels by altering intersubunit interactions

Cyclic nucleotide-gated (CNG) channels are critical for sensory transduction in retinal photoreceptors and olfactory receptor cells; their activity is modulated by phosphoinositides (PIPn) such as phosphatidylinositol 4,5-bisphosphate (PIP2) and phosphatidylinositol 3,4,5-trisphosphate (PIP3). An achromatopsia-associated mutation in cone photoreceptor CNGA3, L633P, is located in a carboxyl (COOH)-terminal leucine zipper domain shown previously to be important for channel assembly and PIPn regulation. We determined the functional consequences of this mutation using electrophysiological recordings of patches excised from cells expressing wild-type and mutant CNG channel subunits. CNGA3-L633P subunits formed functional channels with or without CNGB3, producing an increase in apparent cGMP affinity. Surprisingly, L633P dramatically potentiated PIPn inhibition of apparent cGMP affinity for these channels. The impact of L633P on PIPn sensitivity depended on an intact amino (NH2) terminal PIPn regulation module. These observations led us to hypothesize that L633P enhances PIPn inhibition by altering the coupling between NH2- and COOH-terminal regions of CNGA3. A recombinant COOH-terminal fragment partially restored normal PIPn sensitivity to channels with COOH-terminal truncation, but L633P prevented this effect. Furthermore, coimmunoprecipitation of channel fragments, and thermodynamic linkage analysis, also provided evidence for NH2-COOH interactions. Finally, tandem dimers of CNG...
Source: AJP: Cell Physiology - Category: Cytology Authors: Tags: ARTICLES Source Type: research