What is the name of the protein that binds to calcium in smooth muscle?

Troponin

Explanation:

Troponin and tropomyosin are the two regulatory proteins that are involved in switching the muscle contraction on and off. Troponin protein is a component of the thin filament. At the onset of contraction, the sarcoplasmic reticulum releases calcium ions (Ca2+) into the sarcoplasm. As calcium ions (Ca2+) bind to troponin, it changes shape. This conformational change serves to move the tropomyosin away from myosin-binding sites on actin molecules. Myosin binds to actin and the muscle contraction subsequently begins.