Dissociation of Serum Amyloid P from C4b-Binding Protein and Other Sites by Lactic Acid: Potential Role of Lactic Acid in the Regulation of Pentraxin Function

Abstract

Serum amyloid P (SAP) and C-reactive protein (CRP) are two members of the pentraxin family of proteins. These proteins associate with a variety of other materials that are found in serum under normal or pathological circumstances. This study showed that carboxylated compounds, especially lactic acid, were capable of dissociating pentraxins from several macromolecular binding sites. When measured by sucrose density gradient ultracentrifugation, complete dissociation of the complex of hSAP (human SAP) with C4b-binding protein (C4BP) occurred at > or = 5 mM lactate. Lactate dissociated the hSAP-membrane complex and prevented hSAP self-association. The only interaction that was not dissociated by 10 mM lactate was the hSAP-heparin complex. The relative efficacies of several dissociating agents were O-phosphorylethanolamine > lactate > succinate > carbonate > epsilon-amino-n-caproic acid. This suggested that the carboxyl group plus a hydrogen-bonding site on the hydrocarbon chain was important, but a charged amino group was not a contributor to function when the anion was provided by a carboxyl group. The concentration of lactic acid needed to dissociate hSAP from C4BP was dependent on protein concentration in a manner suggesting the cooperative binding of lactate (coefficient = 2) to hSAP. Pure proteins, at concentrations found in normal serum, required about 12 mM lactate for half-dissociation of the hSAP-C4BP complex. Other pentraxins also interacted with lactic acid, but with lower affinities. An important observation was that lactic acid was capable of dissociating rat CRP from lipoproteins in rat serum. Human CRP bound very weakly to lactate, so that lactate probably is not a significant regulator of this pentraxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum Amyloid P Component Does Not Circulate in Complex with C4‐Binding Protein, Fibronectin or Any Other Major Protein Ligand

“…In conclusion, our results indicate that SAP separated by native analytical separation methods is homogeneous and unliganded. A multitude of ligands may be bound to SAP in vitro [2, 47, 55, 56] but it is unlikely that a major fraction of SAP circulates bound to C4bp or Fn or indeed to a major extent to any other protein ligand in normal serum. The presence of low molecular weight peptide or protein ligands or ligands of other nature (lipids, nucleotides) binding to SAP in serum has previously been reported [57] and these types of ligands cannot be ruled out by the present experimental methods.…”

Pattern Recognition by Pentraxins

“…126–128 SAP, in addition to binding to C1q, also binds to C4b-binding protein. 129 Aggregated SAP and ligand-bound SAP activate the classical pathway of complement. 130,131 The C1q-binding site on SAP is not known.…”

Adaptive diversity of innate immune receptor family short pentraxins in Murinae

“…The ligands for SAP include core polysaccharide moieties of bacterial LPS and phosphoethanolamine (PE) and chemical components on lipid A [29][30][31][32]. The recognition of ligands by short pentraxins initiates a series of innate immune reactions, such as the activation of the classical complement pathway [33,34] and the stimulation of macrophages [12,13,[35][36][37][38].…”