Abstract
Dynamic instability is an intrinsic property of microtubules; however, we do not understand what domains of αβ-tubulins regulate this activity or how these regulate microtubule networks in cells. Here, we define a role for the negatively charged carboxy-terminal tail (CTT) domain of β-tubulin in regulating dynamic instability. By combining in vitro studies with purified mammalian tubulin and in vivo studies with tubulin mutants in budding yeast, we demonstrate that β-tubulin CTT inhibits microtubule stability and regulates the structure and stability of microtubule plus ends. Tubulin that lacks β-tubulin CTT polymerizes faster and depolymerizes slower in vitro and forms microtubules that are more prone to catastrophe. The ends of these microtubules exhibit a more blunted morphology and rapidly switch to disassembly after tubulin depletion. In addition, we show that β-tubulin CTT is required for magnesium cations to promote depolymerization. We propose that β-tubulin CTT regulates the assembly of stable microtubule ends and provides a tunable mechanism to coordinate dynamic instability with ionic strength in the cell.
Highlights
Microtubules are polymers made of repeating subunits of αβ-tubulin heterodimers
Consistent with this, we found that limited proteolysis of purified porcine brain tubulin with subtilisin preferentially removes β-carboxyterminal tail (CTT)
We identify an important role for β-CTT in regulating microtubule dynamics
Summary
Each heterodimer binds four neighboring heterodimers; longitudinal interactions form linear chains known as protofilaments and lateral interactions bind adjacent protofilaments [1]. In this way, heterodimers polymerize into a sheet known as the microtubule lattice, with curvature along the lateral axis that closes the lattice into a cylinder of 11–15 protofilaments with cytosolic and luminal surfaces. Dynamic instability is an intrinsic property of αβ-tubulin heterodimers. It is observed for microtubules assembled in vitro from purified αβ-heterodimers [2, 3, 4] and in living cells [5]. Cells use dynamic instability to organize networks of microtubules and to do work, such as segregating chromosomes during mitosis [6]
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