Which of the following proteins is a principal structural component of elastic fibers?

The principal structural component of elastic fibers is elastin. Elastin is a highly elastic protein that allows tissues in the body to resume their shape after stretching or contracting. It is primarily found in connective tissues and is crucial for the function and resilience of various organs, including the lungs, arteries, and skin. The unique properties of elastin allow it to provide elasticity and flexibility, which is essential for structures that experience frequent or significant deformation.

In contrast, collagen, while also a protein found in connective tissues, primarily provides tensile strength rather than elasticity. Actin and myosin are proteins associated with muscle contraction and are not involved in the structural components of elastic fibers. Understanding the distinct roles of these proteins clarifies why elastin is the correct answer.