Thermodynamic parameters obtained for the formation of the Cas12a-RNA/DNA complex.

The thermodynamics of interactions between Cas12a, RNA, and DNA are important to understanding the molecular mechanisms governing CRISPR-Cas12a's specificity and function. In this study, we employed isothermal titration calorimetry (ITC) and molecular dynamics (MD) simulations to investigate the binding properties and energetic contributions of Cas12a-crRNA complexes with single-stranded (ssDNA) and double-stranded (dsDNA) DNA substrates. ITC analyses revealed significant thermal effects during the interaction of Cas12a-crRNA with ssDNA but no detectable effects with dsDNA. The binding to ssDNA was characterized by an enthalpy change (ΔH°) of -243 ± 18 kcal/mol and a stoichiometry of ∼0.3, indicating partial binding due to structural hindrances such as intramolecular secondary structures in RNA and DNA. MD simulations further supported these findings, highlighting the stability and dynamic behavior of Cas12a-crRNA complexes with both DNA substrates. Binding free energy calculations (MM-GBSA) revealed stronger stabilization of the Cas12a-crRNA complex by dsDNA compared to ssDNA, likely driven by additional electrostatic interactions and protein-DNA contacts. However, these interactions did not produce measurable heat effects in ITC experiments. The combined experimental and computational findings demonstrate that the CRISPR-Cas12a system's interactions with nucleic acids are predominantly governed by their structural characteristics and conformational flexibility. These results deepen our understanding of the thermodynamic and structural principles underlying Cas12a-mediated target recognition and cleavage.