Amyloid deposits stain with Congo red and show apple-green birefringence under polarized light. Chemically, amyloid fibrils share which structural property regardless of their precursor protein?

• A Alpha-helical secondary structure with disulfide cross-links
• B Random coil polypeptide with abundant proline residues
• C Beta-pleated sheet (cross-beta) conformation arranged antiparallel to the fiber axis ✓
• D Triple helix configuration resembling collagen

Explanation

All amyloid proteins, regardless of precursor type (AL, AA, ATTR, etc.), adopt a cross-beta-pleated sheet secondary structure where beta-strands run perpendicular to the fiber axis. This shared conformation is responsible for the characteristic Congo red staining and apple-green birefringence under polarized light, as well as resistance to proteolysis. This structural feature drives self-aggregation and tissue deposition.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.