Abstract
The serum amyloid P component (SAP) is a precursor glycoprotein of amyloid P component found in all types of amyloid deposits. The binding of human SAP to heparan sulfate and dermatan sulfate was studied using Sepharose-immobilized SAP. The apparent dissociation constants of heparan sulfate and dermatan sulfate for immobilized-SAP were estimated to be approximately 2 X 10(-7) M in the presence of 2 mM CaCl2 at neutral pH and physiological ionic strength. Both the binding affinity of SAP for these glycosaminoglycans and the numbers of binding sites of SAP depended on calcium concentration. Cadmium partially substituted for calcium as an activator of glycosaminoglycan binding to SAP. No binding occurs in the absence of added metal, or in the presence of barium, copper, magnesium, manganese, and strontium. The calcium-dependent binding of [3H]heparan sulfate and [3H]dermatan sulfate to SAP was strongly inhibited by heparan sulfate, heparin, and dermatan sulfate. Chondroitin 6-sulfate was a moderate inhibitor, whereas hyaluronic acid, chondroitin 4-sulfate, and keratan sulfate were not potent inhibitors. The calcium-dependent binding of amyloid P component to heparan sulfate and/or dermatan sulfate may be a cause of the coexistence of the particular glycoprotein and these glycosaminoglycans in amyloid tissues.
Highlights
Serum amyloid P component (SAP)/AP binds to isolated amyloid fibrils [10].Recently, it has been shown that millimolar concentrations of cyclic 4,6pyruvate acetal of galactose dissociated AP from human and murine splenic amyloid deposits [21]
After washing with 4 liters of Tris/saline/Ca2+, SAP was eluted from the column with Preparation of 3H-Labeled Glycosaminoglycans-Heparan
SAP fraction was further purified by gel filtration on a column (2.5 x 95 cm) of TSK-GEL HW-65s in Tris/saline/EDTA
Summary
SAP/AP binds to isolated amyloid fibrils [10].Recently, it has been shown that millimolar concentrations of cyclic 4,6pyruvate acetal of galactose dissociated AP from human and murine splenic amyloid deposits [21]. The ligand(s) to which SAP/AP binds in amyloid deposits might be in the nature of carbohydrates but not pyruvate acetal of galactose. On the other hand,heparan sulfate andin some cases dermatan sulfate have been shown to constitute a small but significant and integral part of amyloid tissues [24, 25], and the former is one of the characteristic glycosaminoglycans of normal glomerular basement membranes [26, 27]. I report here that ant eutral pH andphysiological concentration of NaCI, the specific binding of SAP to heparan sulfate and dermatan sulfate occurs inthe presence of calcium. The abbreviations used are: SAP, serum amyloid P component; AP, amyloid P component; BSA, bovine serum albumin
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