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A major challenge emerging in genomic medicine is how to assess best disease risk from rare or novel variants found in disease-related genes. The expanding volume of data generated by very large phenotyping efforts coupled to DNA sequence data presents an opportunity to reinterpret genetic liability of disease risk. Here we propose a framework to estimate the probability of disease given the presence of a genetic variant conditioned on features of that variant. We refer to this as the penetrance, the fraction of all variant heterozygotes that will present with disease. We demonstrate this methodology using a well-established disease-gene pair, the cardiac sodium channel gene SCN5A and the heart arrhythmia Brugada syndrome. From a review of 756 publications, we developed a pattern mixture algorithm, based on a Bayesian Beta-Binomial model, to generate SCN5A penetrance probabilities for the Brugada syndrome conditioned on variant-specific attributes. These probabilities are determined from variant-specific features (e.g. function, structural context, and sequence conservation) and from observations of affected and unaffected heterozygotes. Variant functional perturbation and structural context prove most predictive of Brugada syndrome penetrance.

Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) have emerged as a pivotal model for research. Specialized devices can generate Extracellular Field Potential (EFP) measurements from these cells, analogous to the ventricular complex of the electrocardiogram. However, electrophysiological analysis can be complex and requires specialized expertise, posing a barrier to broader adoption in non-specialized labs. We present the EFP-Analyzer (EFPA), a semi-automized analyzer for EFP traces, which identifies and averages beats, identifies landmarks, and calculates intervals. We demonstrate an analysis of 358 EFP traces from 22 patient-derived lines. We analyzed spontaneously beating iPSC-CMs and optically paced iPSC-CMs through channelrhodopsin. We developed stringent quality criteria and measured EFP intervals, including Field Potential Duration (FPD). We further analyzed the usability and data replicability of EFPA through an inter-intra observer analysis. Correlation coefficient for inter-reader tangent and threshold measurements for these FPD ranged between r: 0.93–1.00. Bland–Altman plots comparing inter observer results for spontaneously beating and paced iPSC-CMs showed 95% limits of agreement (− 13.6 to 19.4 ms and − 13.2 to 15.3 ms, respectively). EFPA could accurately detect FPD prolongation due to drug (moxifloxacin) or pathogenic loss of function mutations (CACNA1C N639T). This program and instructions are available for download at https://github.com/kroncke-lab/EFPA .

The cardiac sodium ion channel (NaV1.5) is a protein with four domains (DI-DIV), each with six transmembrane segments. Its opening and subsequent inactivation results in the brief rapid influx of Na+ ions resulting in the depolarization of cardiomyocytes. The neurotoxin veratridine (VTD) inhibits NaV1.5 inactivation resulting in longer channel opening times, and potentially fatal action potential prolongation. VTD is predicted to bind at the channel pore, but alternative binding sites have not been ruled out. To determine the binding site of VTD on NaV1.5, we perform docking calculations and high-throughput electrophysiology experiments in the present study. The docking calculations identified two distinct binding regions. The first site was in the pore, close to the binding site of NaV1.4 and NaV1.5 blocking drugs in experimental structures. The second site was at the “mouth” of the pore at the cytosolic side, partly solvent-exposed. Mutations at this site (L409, E417, and I1466) had large effects on VTD binding, while residues deeper in the pore had no effect, consistent with VTD binding at the mouth site. Overall, our results suggest a VTD binding site close to the cytoplasmic mouth of the channel pore. Binding at this alternative site might indicate an allosteric inactivation mechanism for VTD at NaV1.5.

Genetic diseases such as ion channelopathies substantially burden human health. Existing treatments are limited and not genotype specific. Here, we report a 2-step high-throughput approach to rapidly identify drug candidates for repurposing as genotype-specific therapy. We first screened 1,680 medicines using a thallium-flux trafficking assay against Kv11.1 gene variants causing long QT syndrome (LQTS), an ion channelopathy associated with fatal cardiac arrhythmia. We identified evacetrapib as a suitable drug candidate that improves membrane trafficking and activates channels. We then used deep mutational scanning to prospectively identify all Kv11.1 missense variants in an LQTS hotspot region responsive to treatment with evacetrapib. Combining high-throughput drug screens with deep mutational scanning establishes a paradigm for mutation-specific drug discovery translatable to personalized treatment of carriers with rare genetic disorders.

Critical to the use of solution NMR to describe the structure and flexibility of membrane proteins is the thorough understanding of the degree of perturbation induced by the detergent or other membrane mimetic. To develop a deeper understanding of the interaction between membrane proteins and micelles or bicelles, we will investigate the differences in structure and flexibility of a model membrane protein TM0026 from Thermotoga maritima using solution NMR. A comparison of the structural differences between TM0026 solubilized in different detergent combinations will provide important insight into the degree of modulation of membrane proteins by detergent physical properties. Here we report the nearly complete backbone and C β resonance assignments of the two transmembrane helical model protein TM0026. These assignments are the first step to using TM0026 to elucidate the interaction between membrane proteins and membrane mimetics.

Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) are an emerging model for determining drug effects and modeling disease. Specialized devices can generate Extracellular Field Potential (EFP) measurements from these cells, analogous to the ventricular complex of the electrocardiogram. The objective of this study was to develop an easy-to-use, easy-to-teach, reproducible software tool to measure EFPs. We present the EFP-Analyzer (EFPA), a semi-automized analyzer for EFP traces, which identifies and averages beats, identifies landmarks, and calculates intervals. We evaluated the tool in an analysis of 358 EFP traces from 22 patient-derived lines. We analyzed spontaneously beating iPSC-CMs, as well as optically paced iPSC-CMs through channelrhodopsin. We developed stringent quality criteria and measured EFP intervals, including Field Potential Duration (FPD). FPD from optically paced iPSC-CMs were shorter than those of spontaneously beating iPSC-CMs (283.7.0±54.2 vs. 293.0±47.5, p: 0.32, respectively). We further analyzed the usability and data replicability of EFPA through an inter-intra observer analysis. Correlation coefficient for inter-reader tangent and threshold measurements for these FPD ranged between r: 0.93-1.00. Bland-Altman plots comparing inter observer results for spontaneously beating and paced iPSC-CMs showed 95% limits of agreement (-13.6 to 19.4ms and -13.2 to 15.3ms, respectively). The EFP-analyzer could accurately detect FPD prolongation due to drug (moxifloxacin) or pathogenic loss of function mutations ( N639T). This program is available for download at https://github.com/kroncke-lab/EFPA . The instructions will be available at the same listed website under the README section of the Github main page. The EFP-Analyzer tool is a useful tool that enables the efficient use of iPSC-CMs as a model to study drug effects and disease.

The cardiac sodium ion channel (Na 1.5) is a protein with four domains (DI-DIV), each with six transmembrane segments. Its opening and subsequent inactivation results in the brief rapid influx of Na ions resulting in the depolarization of cardiomyocytes. The neurotoxin veratridine (VTD) inhibits Na 1.5 inactivation resulting in longer channel opening times, and potentially fatal action potential prolongation. VTD is predicted to bind at the channel pore, but alternative binding sites have not been ruled out. To determine the binding site of VTD on Na 1.5, we perform docking calculations and high-throughput electrophysiology experiments in the present study. The docking calculations identified two distinct binding regions. The first site was in the pore, close to the binding site of Na 1.4 and Na 1.5 blocking drugs in experimental structures. The second site was at the \"mouth\" of the pore at the cytosolic side, partly solvent-exposed. Mutations at this site (L409, E417, and I1466) had large effects on VTD binding, while residues deeper in the pore had no effect, consistent with VTD binding at the mouth site. Overall, our results suggest a VTD binding site close to the cytoplasmic mouth of the channel pore. Binding at this alternative site might indicate an allosteric inactivation mechanism for VTD at Na 1.5.

Critical to the use of solution NMR to describe the structure and flexibility of membrane proteins is the thorough understanding of the degree of perturbation induced by the detergent or other membrane mimetic. To develop a deeper understanding of the interaction between membrane proteins and micelles or bicelles, we will investigate the differences in structure and flexibility of a model membrane protein TM0026 from Thermotoga maritima using solution NMR. A comparison of the structural differences between TM0026 solubilized in different detergent combinations will provide important insight into the degree of modulation of membrane proteins by detergent physical properties. Here we report the nearly complete backbone and C^sub [beta]^ resonance assignments of the two transmembrane helical model protein TM0026. These assignments are the first step to using TM0026 to elucidate the interaction between membrane proteins and membrane mimetics.[PUBLICATION ABSTRACT]

Critical to the use of solution NMR to describe the structure and flexibility of membrane proteins is the thorough understanding of the degree of perturbation induced by the detergent or other membrane mimetic. To develop a deeper understanding of the interaction between membrane proteins and micelles or bicelles, we will investigate the differences in structure and flexibility of a model membrane protein TM0026 from Thermotoga maritima using solution NMR. A comparison of the structural differences between TM0026 solubilized in different detergent combinations will provide important insight into the degree of modulation of membrane proteins by detergent physical properties. Here we report the nearly complete backbone and C sub( beta ) resonance assignments of the two transmembrane helical model protein TM0026. These assignments are the first step to using TM0026 to elucidate the interaction between membrane proteins and membrane mimetics.

Variants in ion channel genes have classically been studied in low-throughput by patch clamping. Deep Mutational Scanning (DMS) is a complementary approach that can simultaneously assess function of thousands of variants. We have developed and validated a method to perform a DMS of variants in SCN5A, which encodes the major voltage-gated sodium channel in the heart. We created a library of nearly all possible variants in a 36 base region of SCN5A in the S4 voltage sensor of domain IV and stably integrated the library into HEK293T cells. In preliminary experiments, challenge with three drugs (veratridine, brevetoxin, and ouabain) could discriminate wildtype channels from gain and loss of function pathogenic variants. High-throughput sequencing of the pre- and post-drug challenge pools was used to count the prevalence of each variant and identify variants with abnormal function. The DMS scores identified 40 putative gain of function and 33 putative loss of function variants. For 8/9 variants, patch clamping data was consistent with the scores. These experiments demonstrate the accuracy of a high-throughput in vitro scan of SCN5A variant function, which can be used to identify deleterious variants in SCN5A and other ion channel genes.