Actin

Actin describes a group of proteins that form microfilaments. Actin is found in almost every cell with a distinct enclosed nucleus. It's commonly found in the structural components of cells and in muscle tissue where it creates the mechanism that allows muscle tissue to contract. It plays a key role in cell division, and is a key component of any part of the body that independently moves, such as the cilia in the lungs. It plays both a role in the healing of tissue, and in the spread of cancer.
Several genetic diseases are related to the production and modulation of actin and can be related to the muscles, heart or the sense of hearing.
Although actin was first observed in the 1880s, it was not isolated as a separate protein until 1942.
Actin at Wikipedia