Structure, Expression, and Evolution of Guinea Pig Serum Amyloid P Component and C-Reactive Protein1

Abstract

The structure and expression of the pentraxins, serum amyloid P component (SAP), and C-reactive protein (CRP), have been investigated in the guinea pig. Northern blot analysis of hepatic RNA from animals in which acute inflammation had been induced by intraperitoneal injection of thioglycollate established that neither SAP or CRP is a major acute phase reactant in the guinea pig. Genomic clones of SAP and CRP were isolated and sequenced, and the gene and the derived protein sequences were compared with other mammalian homologues. Both genes have organizations typical of the pentraxin genes of other species, but some differences were defined in the regions that potentially determine the capacity of the pentraxin gene to be induced during acute inflammation. Nucleotide substitutions in coding regions have occurred at similar rates in the two pentraxin genes. Nonsynonymous substitution rates indicate that SAP and CRP are subject to similar, relatively low levels of constraint; at the amino acid sequence level the rate of evolution is approximately two replacements per site per 10(9) years. An estimate of the phylogenetic relationship among the pentraxin genes suggests that SAP and CRP arose as the result of a gene duplication event that occurred very early in mammalian evolution, but subsequent to the divergence of the reptilian ancestors of the mammalian and avian lineages. This raises doubts about the identity of proteins from fish, which have been previously characterized as CRP and SAP.

Pentraxins in innate immunity: lessons from PTX3

“…Following the identification of CRP, human SAP was identified as its relative on the basis of amino acid sequence identity (51%). Short pentraxins are 25-kDa proteins characterized by a common structural organization in five or ten identical subunits arranged with pentameric radial symmetry (Emsley et al 1994;Rubio et al 1993). CRP and SAP orthologues in various mammal species share substantial sequence similarity but present notable differences in serum basal levels and changes during the acute phase response (e.g.…”

Serum Amyloid P Component Binding to C4b-binding Protein

“…SAP is related in structure to C-reactive protein, and both proteins belong to the pentraxin protein family (9,10). Pentraxins have been highly conserved through evolution and are found in all vertebrate species.…”

Inhibition of Alzheimer β-Peptide Fibril Formation by Serum Amyloid P Component

“…Moreover, in such pathological situations, the attachment of SAP to amyloid fibrils may lead to increased resistance to proteolysis (1,25). SAP has been extremely well conserved through evolution (33) and no deficiency of SAP has been described, suggesting SAP to have important functions. The ability of SAP to inhibit pathological deposition of amyloid-forming peptides may be such a function.…”