Structural effects of an LQT-3 mutation on heart Na+ channel gating

Computational methods that predict three-dimensional structures from amino acid sequences have become increasingly accurate and have provided insights into structure-function relationships for proteins in the absence of structural data. However, the accuracy of computational structural models requires experimental approaches for validation. Here we report direct testing of the predictions of a previously reported structural model of the C-terminus of the human heart Na+ channel. We focused on understanding the structural basis for the unique effects of an inherited C-terminal mutation (Y1795C), associated with long QT syndrome variant 3 (LQT-3), that has pronounced effects on Na+ channel inactivation. Here we provide evidence that this mutation, in which a cysteine replaces a tyrosine at position 1795 (Y1795C), enables the formation of disulfide bonds with a partner cysteine in the channel. Using the predictions of the model, we identify the cysteine and show that three-dimensional information contained in the sequence for the channel protein is necessary to understand the structural basis for some of the effects of the mutation. The experimental evidence supports the accuracy of the predicted structural model of the human heart Na+ channel C-terminal domain and provides insight into a structural basis for some of the mutation-induced altered channel function underlying the disease phenotype.