Setting Right, A Defective Heart Condition

CPVT – Catecholaminergic Polymorphic Ventricular Tachycardia– is a life-threatening heart anomaly caused due to improper electrical activity in the heart. Intense physical strain or emotional stress leads to erratic heartbeats.

Calcium ions are stored in cell structures of the heart muscles. When they move to and fro, a potential gradient is created which triggers the muscles to contract and relax. A protein known as cardiac Calsequestrin (CASQ2) regulates these rhythmic movements by polymerizing or binding to calcium ions. In the next heartbeat, the heart relaxes normally by quick removal of the ions or depolymerizing of CASQ2.

In CPVT, genetic mutations cause defects in CASQ2 protein structure, rendering it unstable. This leads to improper beat-to-beat function of the heart.

A pilot study by Indian researchers explored the possibility of correcting the defective structure of CASQ2. They hypothesized that by suitably introducing small external molecules called pyranones that may attach to the protein interfaces would help in stabilizing it, in turn, regulating the ion flow.

Preliminary results indicate that the synthesized molecules bind well to the protein and facilitate the transfer of calcium ions. In the study, computer simulations were done first to ascertain the ability of the molecules to adhere to CASQ2. After which, 24 small molecules were synthesized.

“Using molecular docking method to design, we synthesized a molecule that had the potential to interact with CASQ2. We then tried to obtain binding mode of the molecule, with the highest biological potential, and found the position at the structure interface which is the key step in CASQ2 polymerization,” explained Dr. Harapriya Chakravarty, the first author of the study, while speaking to India Science Wire.

Next, different gradients of calcium ions were added to purified CASQ2 in a buffer medium to induce polymerization and the uptake was assessed.  Depolymerisation of CASQ2 was simulated by using a chemical– Ethylene Glycol Tetra-acetic Acid or ETGA — which exhibits high affinity to calcium ions. The polymerized CASQ2 protein was found to release the ions in the presence of EGTA. From this, the specific concentration of synthesized molecules that would initiate the re-absorption of the ions was derived.

“We tested the ability of the stabilized CASQ2 compound to resist the EGTA- induced depolymerization. Fifteen out of 24 of the synthesized molecules were active in inhibiting depolymerization of CASQ2 at low concentrations,” said Dr. Naresh Bal, who was involved with biological evaluation tests.

Although it is established that CPVT arises due to altered calcium ion handling, the exact molecular details are still under investigation. This study is a preliminary effort to modify one of the key proteins involved in the process, he added. The team is now looking to take the research forward with cellular studies.

The team included Harapriya Chakravarty, Ashoke Sharon, Chandralata Bal and Monika Yadav (Birla Institute of Technology, Mesra); Naresh C Bal and Nivedita Jena (KIIT University, Bhubaneshwar). The results of the study have been published in journal ACS Omega

Susheela Srinivas

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