Final answer:
Elastin is the protein that allows the skin to return to its original shape after being stretched, distinguishing it for its exceptional elasticity and resilience in the skin and connective tissues.
Step-by-step explanation:
The protein base that helps skin regain its shape after being stretched or expanded is called elastin. This protein is integral to the elastic fibers found in the dermis layer of the skin and other tissues, such as ligaments, where it adds elasticity and resilience. Unlike other structural proteins, elastin allows tissues to stretch and then return to their original shape. It's synthesized from tropoelastin and consists of amino acids that facilitate its rubber-like properties. Organically, elastin works in tandem with collagen, which provides tensile strength to these tissues. Elastin's ability to extend up to one and a half times its resting length and snap back to its initial form is fundamental for the various types of connective tissues that require flexibility as well as firmness.