Key result
The T153I mutation in the Kir7.1 channel resulted in negligible K+ conductance and failed to hyperpolarize the membrane potential, indicating a dysfunctional inner pore.
Why the study?
A T153I substitution in the Kir7.1 protein causes blindness, but whether it alters translation, localization, or ion transport properties was unknown.
The T153I mutation in the Kir7.1 channel alters the inner pore radius, resulting in negligible K+ conductance and channel dysfunction.
T153I Kir7.1 dysfunction may underlie channelopathy phenotypes; leaves open clinical translation and requires in vivo validation.
Inward-rectifier potassium channel 7.1 (Kir7.1) is present in the polarized epithelium, including the retinal pigmented epithelium. A single amino acid change at position 153 in the KCNJ13 gene, a substitution of threonine to isoleucine in the Kir7.1 protein, causes blindness. We hypothesized that the disease caused by this single amino acid substitution within the transmembrane protein domain could alter the translation, localization, or ion transport properties. We assessed the effects of amino acid side-chain length, arrangement, and polarity on channel structure and function. We showed that the T153I mutation yielded a full-length protein localized to the cell membrane. Whole cell patch-clamp recordings and chord conductance analyses revealed that the T153I mutant channel had negligible K + conductance and failed to hyperpolarize the membrane potential. However, the mutant channel exhibited enhanced inward current when rubidium was used as a charge carrier, suggesting that an inner pore had formed and the channel was dysfunctional. Substituting with a polar, nonpolar, or short side-chain amino acid did not affect the localization of the protein. Still, it had an altered channel function due to differences in pore radius. Polar side chains (cysteine and serine) with inner pore radii comparable to wildtype exhibited normal inward K + conductance. Short side chains (glycine and alanine) produced a channel with wider than expected inner pore size and lacked the biophysical characteristics of the wild-type channel. Leucine substitution produced results similar to the T153I mutant channel. This study provides direct electrophysiological evidence for the structure and function of the Kir7.1 channel’s narrow inner pore in regulating conductance.
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Beverley et al. (2022) studied Blindness associated with KCNJ13 gene mutation. T153I mutation in Kir7.1 protein vs. Wild-type Kir7.1 channel was evaluated on K+ conductance and channel function. The T153I mutation in the Kir7.1 channel resulted in negligible K+ conductance and failed to hyperpolarize the membrane potential, indicating a dysfunctional inner pore.
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