Biophysical studies have shown that each molecule of calsequestrin 1 (CASQ1) can bind about 70–80 Ca²⁺ ions. However, the nature of Ca²⁺-binding sites has not yet been fully characterized. In this study, we employed in silico approaches to identify the Ca²⁺ binding sites and to understand the molecular basis of CASQ1–Ca²⁺ recognition. We built the protein model by extracting the atomic coordinates for the back-to-back dimeric unit from the recently solved hexameric CASQ1 structure (PDB id: 3UOM) and adding the missing C-terminal residues (aa350–364). Using this model we performed extensive 30 ns molecular dynamics simulations over a wide range of Ca²⁺ concentrations ([Ca²⁺]). Our results show that the Ca²⁺-binding sites on CASQ1 differ both in affinity and geometry. The high affinity Ca²⁺-binding sites share a similar geometry and interestingly, the majority of them were found to be induced by increased [Ca²⁺]. We also found that the system shows maximal Ca²⁺-binding to the CAS (consecutive aspartate stretch at the C-terminus) before the rest of the CASQ1 surface becomes saturated. Simulated data show that the CASQ1 back-to-back stacking is progressively stabilized by the emergence of an increasing number of hydrophobic interactions with increasing [Ca²⁺]. Further, this study shows that the CAS domain assumes a compact structure with an increase in Ca²⁺ binding, which suggests that the CAS domain might function as a Ca²⁺-sensor that may be a novel structural motif to sense metal. We propose the term “D_n-motif” for the CAS domain.

Microtubule associated serine/threonine kinase (MASTL) is an important Ser/Thr kinase belonging to the family of AGC kinases. It is the human orthologue of Greatwall kinase (Gwl) that plays a significant role in mitotic progression and cell cycle regulation. Upregulation of MASTL in various cancers and its association with poor patient survival establishes it as an important drug target in cancer therapy. Nevertheless, the target remains unexplored with the paucity of studies focused on identification of inhibitors against MASTL, which emphasizes the relevance of our present study. We explored various drug databases and performed virtual screening of compounds from both natural and synthetic sources. A list of promising compounds displaying high binding characteristics towards MASTL protein is reported. Among the natural compounds, we found a 6-hydroxynaphthalene derivative ZINC85597499 to display best binding energy value of −9.32 kcal/mol. While among synthetic compounds, a thieno-pyrimidinone based tricyclic derivative ZINC53845290 compound exhibited best binding affinity of value −7.85 kcal/mol. MASTL interactions with these two compounds were further explored using molecular dynamics simulations. Altogether, this study identifies potential inhibitors of human Gwl kinase from both natural and synthetic origin and calls for studying these compounds as potential drugs for cancer therapy.