Final answer:
Myosin plays a crucial role in the contraction of both smooth and striated muscle by pulling actin, which is essential in the muscle contraction mechanism. While specific proteins like troponin and calmodulin regulate contraction in different muscle types, myosin is the one directly involved in the contraction process in both. Option e. Myosin light chains is the correct answer.
Step-by-step explanation:
The muscle protein that plays an important role in the contraction of both smooth and striated muscle is myosin. In the process of muscle contraction for striated muscle, which includes skeletal and cardiac muscles, myosin pulls on actin after specific binding sites on actin are exposed due to the interaction between calcium ions and proteins like troponin and tropomyosin.
Unlike striated muscle, smooth muscle does not contain troponin. Instead, the regulatory protein calmodulin plays a crucial role in the contraction process here, by forming a complex with calcium that activates myosin (light chain) kinase, leading to the phosphorylation and activation of myosin heads which can then bind to actin and initiate contraction.
Considering the options provided by the student, troponin is specific to striated muscle, and myosin light chains are specific to smooth muscle, but myosin and actin are fundamental to the contraction mechanism in both types of muscle. However, myosin is the one directly involved in the pulling action that results in muscle contraction. Hence, myosin is the protein that is critical in both types of muscle for contraction. Therefore, the correct option is e. Myosin light chains.