Amyloid P component (AP) is a naturally occurring glycoprotein that is
found in serum and basement membranes, AP is also a component of all
types of amyloid, including that found in individuals who suffer from
Alzheimer's disease and Down's syndrome. Because AP has been found to
bind strongly and specifically to certain glycosaminoglycans that are
components of amyloid deposits, AP may play an important role in the m
aintenance of amyloid. In the present work, we isolated and identified
two proteolytic fragments of AP that are responsible for its heparin-
binding activity. Neither fragment corresponds to published heparin-bi
nding sequences. The structural requirements for activity of the pepti
des (amino acid residues 27-38 and 192-203 of AP) were examined by mea
ns of solid-phase inhibition assays with synthetic peptides, AP-(192-2
03)-peptide inhibits the Ca2+-dependent binding of AP to heparin with
an IC50 of 25 mu M, while the IC50 of AP-(27-38)-peptide and AP-(33-38
)-peptide are 10 mu M and 2 mu M, respectively, The understanding of t
he structure and function of active AP peptides will be useful for dev
elopment of amyloid-targeted diagnostics and therapeutics.