Direct interaction between tubulin and PMCA, a complex with functional implications

Tubulin exerts regulatory functions through interactions with various noncytoskeletal proteins, modulating their activity and contributing to diverse cellular processes. Here, we investigated the direct interaction between tubulin and plasma membrane Ca²⁺-ATPase (PMCA), a transporter involved in intracellular Ca²⁺ homeostasis. We demonstrated that tubulin directly associates with PMCA in a high-molecular-weight tubulin-PMCA complex, independently of tubulin polymerization, indicating that the dimeric form is sufficient for binding. Functional characterization of PMCA revealed a tubulin concentration-dependent stimulation of PMCAs ATPase and p-nitrophenylphosphatase activities. Conversely, PMCA affected microtubule polymerization in microtubule-enriched preparations. These findings reveal a direct interaction where tubulin modulates the activity of PMCA, and PMCA alters tubulin assembly/polymerization, providing insights into this novel complex and establishing a framework for further investigation.