In addition to the main fibril peptide, mature amyloid fibrils have additional components. Serum amyloid P component (SAP) binds to all types of amyloid fibrils and is a universal constituent of amyloid deposits. SAP binding protects amyloid fibrils from proteolytic degradation (Tennent et al. 1995, Westermark 2005). SAP may function as a chaperone for amyloid formation (Coker et al. 2000).
Glycosaminoglycans (GAGs) and proteoglycans are found associated with all types of amyloid deposits (Alexandrescu 2005). Of the different types of GAG heparan sulfate and dermatan sulfate are the most prominent in amyloid deposits (Hirschfield & Hawkins, 2003). GAGs have been implicated in the nucleation of fibrils, they can also stabilize mature fibrils against dissociation (Yamaguchi et al. 2003) and proteolytic degradation (Gupta-Bansal et al. 1995).
Perlecan coimmunolocalizes with all types of amyloids (Snow & Wright 1989), accelerating fibril formation (Castillo et al. 1998), stabilizing them once formed (Castillo et al. 1997), and protecting them from proteolytic degradation (Gupta-Bansal et al. 1995).
APOE isoform 4 binds tightly to soluble ABeta peptide forming complexes that resist dissociation; it also binds to ABeta in its fibril form (Bales et al. 2002).