What is the function of PDZ domain proteins?

• A. To recognize internal elements of junctions to initiate cell signaling pathways
• B. To anchor cells to basement membrane
• C. To form the adhesive core of desmosomes
• D. To facilitate actin polymerization

Answer: (A)

PDZ domain proteins act as scaffolds at cell junctions, bringing together membrane proteins, kinases, and other signaling molecules to create organized signaling complexes right at the membrane. By binding to specific motifs on junctional proteins, they localize and assemble the components needed to initiate and regulate signaling pathways inside the cell. This is why recognizing junctional elements to coordinate downstream signaling is the most accurate description. The other roles described are carried out by different proteins: integrins and their ligands anchor cells to the basement membrane; desmosomes are built from cadherin–catenin networks that provide strong adhesion; and actin polymerization is driven by actin-regulating proteins rather than PDZ scaffolds themselves.