Which protein is necessary for the construction of microtubules?

Tubulin is the fundamental building block of microtubules, which are part of the cytoskeleton in eukaryotic cells. Microtubules play critical roles in maintaining cell shape, providing structural support, and facilitating intracellular transport and cell division. Tubulin exists as two related proteins: alpha-tubulin and beta-tubulin, which dimerize to form the protofilaments that make up microtubules.

In contrast, actin and myosin are primarily involved in muscle contraction and the maintenance of cell shape, but they are not structural components of microtubules. Collagen is a protein found in connective tissues, providing tensile strength and structural support, but it does not play a role in the formation of microtubules. Therefore, tubulin is specifically required for the assembly and stability of microtubule structures within cells.