Inhibits fibrillization of amyloid-beta peptide during the elongation phase. Has also been shown to assemble amyloid fibrils into protease-resistant aggregates. Binds heparin. {ECO:0000269|PubMed:15522881, ECO:0000269|PubMed:15615705, ECO:0000269|PubMed:15853808, ECO:0000269|PubMed:16300410}. This is the function of ENSG00000188517 (COL25A1, collagen type XXV alpha 1 chain).