Which protein serves a structural role in skin, hair, and nails?

The correct choice, keratin, is a key structural protein that plays a vital role in the composition of skin, hair, and nails. This fibrous protein is known for its strength and resilience, providing support and protection. In skin, keratin contributes to the outer layer, making it more durable and resistant to damage, while in hair and nails, it forms the primary structural component, lending both rigidity and toughness.

Collagen, while also a structural protein found in the skin, primarily provides elasticity and firmness rather than the hard structural integrity that keratin does. Elastin is responsible for the elasticity of skin and tissues but does not contribute to hardness or protective layers like keratin. Actin, on the other hand, is a protein involved mainly in muscle contraction and is not significant in the structural composition of skin, hair, or nails. Thus, keratin stands out as the main protein that fulfills the specific structural role in these tissues.