Which protein works alongside actin to convert chemical energy into mechanical energy in muscle cells?

Myosin is a motor protein that plays a crucial role in muscle contraction by interacting with actin filaments. In muscle cells, the process of converting chemical energy into mechanical energy is primarily driven by ATP (adenosine triphosphate). When ATP is hydrolyzed, it causes conformational changes in the myosin head, allowing it to bind to actin and perform a power stroke — a movement that slides the actin filaments past myosin, resulting in muscle contraction.

This interaction is essential for muscle function; without myosin, the structural dynamics that facilitate muscle contraction would be compromised. While the other proteins listed have important roles in muscle function—myoglobin stores oxygen, titin provides structural support, and collagen adds strength and elasticity—none are involved directly in the conversion of chemical energy to mechanical work in muscle contraction in the way that myosin is. This specificity in function is what makes myosin the key protein in this biological process.