The mechanism of LQTS related CaM mutation E141G interfering with Ca1.2 channels function through its C-lobe.

Mutations in the CALM1-3 genes, which encode calmodulin (CaM), have been reported in clinical cases of long QT syndrome (LQTS). Specifically, the CaM mutant E141G (CaM) in the variant CALM1 gene has been identified as a causative factor in LQTS. This mutation disrupts the normal Ca-dependent inactivation (CDI) function of Ca1.2 channels. However, it is still unclear how CaM interferes with the regulatory role of wild-type (WT) CaM on Ca1.2 channels and leads to abnormal CDI. A CaM molecule contains two lobes with similar structure, the N-lobe and the C-lobe. In this study, a CaM-truncated C-lobe mutant E141G (C-lobe) was engineered to exclude the impact of the unmutated N-lobe. Our findings revealed that at low Ca concentration ([Ca]), the binding of C-lobe to the preIQ, IQ and N-terminus (NT) of Ca1.2 channels has higher binding capacity (B: 0.17, 0.22, 0.13) compared with those of WT C-lobe (B: 0.04, 0.14, 0.11) in GST pull-down assay. With an increase in [Ca], the Ca-dependency for C-lobe binding to Ca1.2 channels was impaired. Moreover, C-lobe induced the relative channel activity to 240.58 ± 51.37% at resting [Ca], but it was unable to diminish the channel activity at high [Ca] even in the presence of WT N-lobe, which may be responsible for the abnormal CDI of Ca1.2 channels affected by the LQTS-related CaM mutation. Our research provides preliminary insights into the mechanism by which the CaM mutation interferes with Ca1.2 channels function through its C-lobe.