The cytoskeleton protein that primarily helps a cell maintain its shape is intermediate filaments.

Here's why:

* Intermediate filaments are strong, rope-like fibers that provide structural support and resist tension. They form a network throughout the cytoplasm, anchoring organelles and providing a framework for the cell.

* Microtubules are involved in cell movement, organelle transport, and cell division. They are more dynamic than intermediate filaments.

* Actin filaments are involved in cell movement and shape changes. They are also more dynamic than intermediate filaments.

While microtubules and actin filaments play roles in cell shape, their primary functions lie elsewhere. Intermediate filaments are the most directly involved in maintaining the overall structural integrity and shape of a cell.