What structural feature of integrins allows them to mediate signals between cells and the extracellular matrix?

• A. Integrins are embedded only in the intracellular membrane.
• B. Integrins are exclusively found in the cytoplasm.
• C. Integrins are soluble proteins that float freely in the extracellular matrix.
• D. Integrins have subunits that span the plasma membrane, connecting intracellular and extracellular environments.

Answer: (D)