Molecular dynamics simulation of TMEM16A channel: Linking structure with gating

Anoctamin-1 is a core component of a mechanosensory anion channel complex in C. elegans

Mechanotransduction channels are widely expressed in both vertebrates and invertebrates, mediating various physiological processes such as touch, hearing and blood-pressure sensing. While previously known mechanotransduction channels in metazoans are primarily cation-selective, we identified Anoctamin-1 (ANOH-1), the C. elegans homolog of mammalian calcium-activated chloride channel ANO1/TMEM16A, as an essential component of a mechanosensory channel complex that contributes to the nose touch mechanosensation in C. elegans. Ectopic expression of either C. elegans or human Anoctamin-1 confers mechanosensitivity to touch-insensitive neurons, suggesting a cell-autonomous role of ANOH-1/ANO1 in mechanotransduction. Additionally, we demonstrated that the mechanosensory function of ANOH-1/ANO1 relies on CIB (calcium- and integrin- binding) proteins. Thus, our results reveal an evolutionarily conserved chloride channel involved in mechanosensory transduction in metazoans, highlighting the importance of anion channels in mechanosensory processes.

Key Interaction Changes Determine the Activation Process of Human Parathyroid Hormone Type 1 Receptor

The parathyroid hormone type 1 receptor (PTH1R) plays a crucial role in modulating various physiological functions and is considered an effective therapeutic target for osteoporosis. However, a lack of detailed molecular and energetic information about PTH1R limits our comprehensive understanding of its activation process. In this study, we performed computational simulations to explore key events in the activation process, such as conformational changes in PTH1R, Gs protein coupling, and the release of guanosine diphosphate (GDP). Our analysis identified kinetic information, including the rate-determining step, transition state, and energy barriers. Free-energy and structural analyses revealed that GDP could be released from the Gs protein when the binding cavity is partially open. Additionally, we predicted important residues, including potential pathogenic mutations, and verified their significance through site-directed mutations. These findings enhance our understanding of class B GPCR activation mechanisms. Furthermore, the methodology employed in this study can be applied to other biophysical systems.

Structural and theoretical basis for drug development targeting TMEM16A: Inhibition mechanism of tracheloside analogs

Ion channels play a crucial role in the electrophysiological activities of organisms. The calcium-activated chloride channel TMEM16A is involved in various physiological processes. Therefore, inhibitors of TMEM16A are used to treat diseases caused by TMEM16A dysfunction. However, the unclear inhibition mechanism hinders the progress of drug development. Based on our previous study, we found that the molecular structures of TMEM16A inhibitors tracheloside, matairesinoside and arctigenin are similar. In this study, we conducted a structure-based virtual screening of tracheloside analogs from the PubChem database. The six tracheloside analogs with the highest affinity to TMEM16A were selected, and their inhibitory effects were detected by fluorescence and electrophysiological experiments. Subsequently, the interaction between the tracheloside analogs and TMEM16A was investigated through molecular docking and site-directed mutagenesis. Based on the above results, the mechanism of inhibition of TMEM16A gated conformation by tracheloside analogs was proposed. These findings provide a structural and theoretical basis for drug development targeting TMEM16A.

Predicting Mutational Effects on Ca2+-Activated Chloride Conduction of TMEM16A Based on a Simulation Study

The dysfunction and defects of ion channels are associated with many human diseases, especially for loss-of-function mutations in ion channels such as cystic fibrosis transmembrane conductance regulator mutations in cystic fibrosis. Understanding ion channels is of great current importance for both medical and fundamental purposes. Such an understanding should include the ability to predict mutational effects and describe functional and mechanistic effects. In this work, we introduce an approach to predict mutational effects based on kinetic information (including reaction barriers and transition state locations) obtained by studying the working mechanism of target proteins. Specifically, we take the Ca2+-activated chloride channel TMEM16A as an example and utilize the computational biology model to predict the mutational effects of key residues. Encouragingly, we verified our predictions through electrophysiological experiments, demonstrating a 94% prediction accuracy regarding mutational directions. The mutational strength assessed by Pearson's correlation coefficient is -0.80 between our calculations and the experimental results. These findings suggest that the proposed methodology is reliable and can provide valuable guidance for revealing functional mechanisms and identifying key residues of the TMEM16A channel. The proposed approach can be extended to a broad scope of biophysical systems.

Identification of a druggable pocket of the calcium-activated chloride channel TMEM16A in its open state

The calcium-activated chloride channel TMEM16A is a potential drug target to treat hypertension, secretory diarrhea, and several cancers. However, all reported TMEM16A structures are either closed or desensitized, and direct inhibition of the open state by drug molecules lacks a reliable structural basis. Therefore, revealing the druggable pocket of TMEM16A exposed in the open state is important for understanding protein-ligand interactions and facilitating rational drug design. Here, we reconstructed the calcium-activated open conformation of TMEM16A using an enhanced sampling algorithm and segmental modeling. Furthermore, we identified an open state druggable pocket and screened a potent TMEM16A inhibitor, etoposide, which is a derivative of a traditional herbal monomer. Molecular simulations and site-directed mutagenesis showed that etoposide binds to the open state of TMEM16A, thereby blocking the ion conductance pore of the channel. Finally, we demonstrated that etoposide can target TMEM16A to inhibit the proliferation of prostate cancer PC-3 cells. Together, these findings provide a deep understanding of the TMEM16A open state at an atomic level and identify pockets for the design of novel inhibitors with broad applications in chloride channel biology, biophysics, and medicinal chemistry.

Dawn of a New Era for Membrane Protein Design

A major advancement has recently occurred in the ability to predict protein secondary structure from sequence using artificial neural networks. This new accessibility to high-quality predicted structures provides a big opportunity for the protein design community. It is particularly welcome for membrane protein design, where the scarcity of solved structures has been a major limitation of the field for decades. Here, we review the work done to date on the membrane protein design and set out established and emerging tools that can be used to most effectively exploit this new access to structures.

Gating and Regulatory Mechanisms of TMEM16 Ion Channels and Scramblases

The transmembrane protein 16 (TMEM16) family consists of Ca2+-activated ion channels and Ca2+-activated phospholipid scramblases (CaPLSases) that passively flip-flop phospholipids between the two leaflets of the membrane bilayer. Owing to their diverse functions, TMEM16 proteins have been implicated in various human diseases, including asthma, cancer, bleeding disorders, muscular dystrophy, arthritis, epilepsy, dystonia, ataxia, and viral infection. To understand TMEM16 proteins in health and disease, it is critical to decipher their molecular mechanisms of activation gating and regulation. Structural, biophysical, and computational characterizations over the past decade have greatly advanced the molecular understanding of TMEM16 proteins. In this review, we summarize major structural features of the TMEM16 proteins with a focus on regulatory mechanisms and gating.