The microtubule cytoskeleton is a dynamic network essential for many cellular processes, influenced by physicochemical factor such as temperature, pH, dimer concentration and ionic environment. In this study, we used in vitro reconstitution assays to examine the effects of four monovalent ions (Na ⁺ , K ⁺ , Cl ^- , and Ac ^- ) on microtubule dynamics, uncovering distinct effects for each ion. Na ⁺ was found to increase microtubule dynamicity by raising catastrophe frequency, polymerization and depolymerization speeds, ultimately reducing microtubule lifetime by 80 %. Conversely, Ac boosts microtubule nucleation and stabilizes microtubules by increasing rescue frequency and preventing breakages, resulting in longer microtubules with extended lifetimes. Cl ^- appeared to potentiate the effects of Na ⁺ , while K ⁺ had minimal impact on microtubule dynamic parameters. These findings demonstrate that Na ⁺ and Ac ^- have opposing effects on microtubule dynamics, with Na ⁺ destabilizing and Ac ^- stabilizing the microtubule structure. This ionic impact is mainly through modulation of tubulin-tubulin interactions rather than affecting the hydrolysis rate. In conclusion, ion identity plays a crucial role in modulating microtubule dynamics. Understanding the ionic environment is essential for microtubule-related research, as it significantly influences microtubule behavior, stability, and interactions with other proteins.

SIGNIFICANCE STATEMENT

The microtubule cytoskeleton is vital for cellular processes and influenced by temperature, pH, dimer concentration, and ionic environment. Understanding how these physicochemical factors regulate microtubule polymerization is crucial for elucidating microtubule dynamics and stability. Our in vitro reconstitution assays reveal that Na ⁺ and Ac ^- ions have opposing effects on microtubule dynamics. Na ⁺ increases dynamicity by raising catastrophe frequency and reducing lifetime by 80 %, while Ac ^- enhances nucleation and stability, resulting in longer microtubules. Cl ^- potentiates the effects of Na ⁺ , and K ⁺ has minimal impact. Our findings highlight that ion identity crucially modulates microtubule dynamics, significantly influencing stability and interactions.