Binding specificity of serum amyloid P component for the pyruvate acetal of galactose.

Serum amyloid P component (SAP) is a normal plasma protein that is of interest because of its presence in amyloid deposits, its presence in normal human glomerular basement membrane, and its stable evolutionary conservation. It has calcium-dependent ligand-binding specificity for amyloid fibrils, fibronectin (Fn), C4-binding protein (C4bp), and agarose. Although the binding to agarose, a linear galactan hydrocolloid derived from some marine algae, is unlikely per se to be related to the physiological function of SAP, it does provide a model system in which to explore the precise ligand requirements of SAP. We report here that the amount of SAP from human, mouse, and plaice (Pleuronectes platessa L.) serum able to bind to agarose from different sources reflect precisely their pyruvate content. Methylation with diazomethane of the carboxyl groups in the pyruvate moiety of agarose completely abolishes SAP binding to agarose. The pyruvate in agarose exists as the 4,6-pyruvate acetal of beta-D-galactopyranose. We have therefore synthesized this galactoside, using a novel procedure, established its structure by analysis of its nuclear magnetic resonance spectra, and shown that it completely inhibits all known calcium-dependent binding reactions of SAP. The R isomer of the cyclic acetal, methyl 4,6-O-(1-carboxyethylidene)-beta-D-galactopyranoside (MO beta DG) was effective at millimolar concentration and was more potent than its noncyclic analogue, while pyruvate, D-galactose, and methyl beta-D-galactopyranoside were without effect. The autologous protein ligands of SAP presumably, therefore express a structural determinant(s) that stereochemically resembles MO beta DG. Availability of this specific, well-characterized, low molecular weight ligand for SAP should facilitate further investigation of the function of SAP and its role in physiological and pathophysiological processes.

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Studies with Radiolabelled Serum Amyloid P Component Provide Evidence for Turnover and Regression of Amyloid Deposits In Vivo

Clinical Science ◽

10.1042/cs0870289 ◽

1994 ◽

Vol 87 (3) ◽

pp. 289-295 ◽

Cited By ~ 53

Author(s):

Philip N. Hawkins

Keyword(s):

Amyloid Fibrils ◽

Specific Binding ◽

Serum Amyloid ◽

Poor Correlation ◽

Amyloid P Component ◽

Serum Amyloid P ◽

Serum Amyloid P Component ◽

Amyloid Deposits ◽

Amyloid P

1. Quantitative scintigraphic and turnover studies, utilizing the specific binding affinity of serum amyloid P component for amyloid fibrils, have been developed as a tool for evaluating amyloid deposits in vivo. 2. Serial studies in over 300 patients have shown characteristic, diagnostic tissue distributions of amyloid in different types of amyloidosis. There is generally a poor correlation between quantity of amyloid and associated organ dysfunction. 3. Contrary to previous expectations, regression of amyloid has been demonstrated systematically for the first time: AA, AL and variant transthyretin-associated amyloid deposits often regress rapidly, and sometimes completely, if the supply of fibril protein precursors is substantially reduced.

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Amyloidosis

Oxford Textbook of Medicine ◽

10.1093/med/9780198746690.003.0241 ◽

2020 ◽

pp. 2218-2234

Author(s):

Mark B. Pepys ◽

Philip N. Hawkins

Keyword(s):

Amyloid Fibrils ◽

Amyloid Fibril ◽

Polarized Light ◽

Serum Amyloid ◽

Amyloid P Component ◽

Serum Amyloid P ◽

Serum Amyloid P Component ◽

Amyloid Deposits ◽

Amyloid P

Amyloidosis is the clinical condition caused by extracellular deposition of amyloid in the tissues. Amyloid deposits are composed of amyloid fibrils, abnormal insoluble protein fibres formed by misfolding of their normally soluble precursors. About 30 different proteins can form clinically or pathologically significant amyloid fibrils in vivo as a result of either acquired or hereditary abnormalities. Small, focal, clinically silent amyloid deposits in the brain, heart, seminal vesicles, and joints are a universal accompaniment of ageing. Clinically important amyloid deposits usually accumulate progressively, disrupting the structure and function of affected tissues and lead inexorably to organ failure and death. There is no licensed treatment which can specifically clear amyloid deposits, but intervention which reduces the availability of the amyloid fibril precursor proteins can arrest amyloid accumulation and may lead to amyloid regression with clinical benefit. Pathology—amyloid fibrils bind Congo red dye producing pathognomonic green birefringence when viewed in high-intensity cross-polarized light, and the protein type can be identified by immunostaining or proteomic analysis. Amyloid deposits always contain a nonfibrillar plasma glycoprotein, serum amyloid P component, the universal presence of which is the basis for use of radioisotope-labelled serum amyloid P component as a diagnostic tracer. Clinicopathological correlation—amyloid may be deposited in any tissue of the body, including blood vessels walls and connective tissue matrix; clinical manifestations are correspondingly diverse. Identification of the amyloid fibril protein is always essential for appropriate clinical management. The specific types of amyloidosis covered in this chapter are reactive systemic (AA) amyloidosis, monoclonal immunoglobulin light chain (AL) amyloidosis, and hereditary systemic amyloidoses (including familial amyloid polyneuropathy).

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