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.
The algal polysaccharides, agar, agarose, carrageenan, and algin, have played and are continuing to play a significant role in advancing the state of the art in biotechnology. Agar and its more neutral component, agarose, have been and continue to be particularly Important in biomedical research and diagnosis of disease states. More recently, agar has been used extensively as a medium for cloning genetically engineering microorganisms, as well. At present, agarose is the only known thermoreversible, ion-independent gelling agent. Agarose can be prepared with consistent properties, is essentially neutral chemically, and forms strong aqueous gels at low concentrations. Because of these characteristics, mapping of gene fragments and separation prior to insertion In plasmids, as well as providing an excellent medium for plant and animal cell culture and affinity separations, have been added to the ever-increasing number of applications for agarose. Low gelling-melting temperature hydroxyethyl, as well as other unique derivatives, have further extended agarose's indispensibility in biotechnology.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.