A cyclic nucleotide-gated channel mutation associated with canine daylight blindness provides insight into a role for the S2 segment Tri-Asp motif in channel biogenesis

摘要: Cone cyclic nucleotide-gated channels are tetramers formed by CNGA3 and CNGB3 subunits; subunits function as homotetrameric but exhibits channel only when co-expressed with CNGA3. An aspartatic acid (Asp) to asparagine (Asn) missense mutation at position 262 in the canine (D262N) subunit results loss of cone (daylight blindness), suggesting an important role for this aspartic residue biogenesis and/or function. Asp is located a conserved region second transmembrane segment containing three residues designated Tri-Asp motif. This motif all CNG channels. Here we examine mutations homomeric using combination experimental computational approaches. Mutations these result absence nucleotide-activated currents heterologous expression. A fluorescent tag on shows mislocalization mutant Co-expressing mutants wild type some functional channels, however, their electrophysiological characterization matches properties failure record heteromeric suggests that Asp/Asn affect assembly. homology model S1–S6 was generated relaxed membrane molecular dynamics simulations. The predicts involved non-specific salt bridge pairings positive S3/S4. We propose D262N dogs CNGB3-day blindness inter-helical interactions altering electrostatic equilibrium within S1–S4 bundle. Because analogous voltage-gated Shaker potassium family were implicated monomer folding, hypothesize destabilizing impairs folding state during biogenesis.