Final answer:
Actin is the globular protein that forms the thin filament in skeletal muscle cells, which works in tandem with the thick myosin filament to facilitate muscle contraction.
Step-by-step explanation:
The protein that forms the thin filament in a skeletal muscle cell is actin. In muscle contraction, the actin thin protein filament slides over the thick myosin filament. The myosin-binding site on actin is blocked by tropomyosin when muscles are relaxed. This prevents actin-myosin interaction, which is necessary for muscle contraction. When calcium ions (Ca²⁺) bind to the troponin complex, it causes a conformational change that moves tropomyosin away from the myosin-binding sites on actin, allowing muscle contraction to proceed.