Ca2+-dependent Binding of Human Serum Amyloid P Component to Alzheimer's β-Amyloid Peptide

Serum amyloid P component (SAP), a normal glycoprotein, is universally found in amyloid deposits, including cerebrovascular amyloid of Alzheimer’s disease. This paper describes the Ca2+-dependent binding of human SAP to Alzheimer’s β-amyloid peptide (Aβ). 125I-SAP binds to synthetic human Aβ-(1–40) immobilized on microtiter plates at a dissociation constant of 6.0 × 10–9M in 0.01 M MRIs-ACL, 0.15M NaCl, pH 7.5, containing 2 mM Ca2+, 1% bovine serum albumin, and 0.05% Tween 20. Binding inhibition assay has shown that soluble Aβ-(1–40) and Aβ-(1–28) also bind to SAP. Since SAP is resistant to proteases in the presence of calcium, the Ca2+-dependent binding of SAP to soluble Aβ and to β-amyloid fibrils would give pathological effects on fibril formation and persistence of β-amyloid in Alzheimer’s disease. Serum amyloid P component (SAP), a normal glycoprotein, is universally found in amyloid deposits, including cerebrovascular amyloid of Alzheimer’s disease. This paper describes the Ca2+-dependent binding of human SAP to Alzheimer’s β-amyloid peptide (Aβ). 125I-SAP binds to synthetic human Aβ-(1–40) immobilized on microtiter plates at a dissociation constant of 6.0 × 10–9M in 0.01 M MRIs-ACL, 0.15M NaCl, pH 7.5, containing 2 mM Ca2+, 1% bovine serum albumin, and 0.05% Tween 20. Binding inhibition assay has shown that soluble Aβ-(1–40) and Aβ-(1–28) also bind to SAP. Since SAP is resistant to proteases in the presence of calcium, the Ca2+-dependent binding of SAP to soluble Aβ and to β-amyloid fibrils would give pathological effects on fibril formation and persistence of β-amyloid in Alzheimer’s disease.