Proteins, proteomics

serum amyloid P component

Serum amyloid P component (SAP) is an acute phase protein, structurally related to C-reactive protein, which is synthesized in response to pro-inflammatory cytokines early in the inflammatory response. SAP interacts with inflammatory and complement factors, acting as an opsonin that reacts with nuclear autoantigens in systemic autoimmunity. [s]

acute phase : Alzheimer's : amyloid : amyloidoses : AP : autoimmunity : complement : CRP : cytokines : evolution : inflammation : neurofibrillary tangles : opsonin : pentraxin proteins : plaques : PTX3 : SAP

SAP is the serum form of amyloid P component (AP), a 25kD pentameric, short pentraxin protein first identified in pathological deposits termed "amyloid". Pentraxin proteins exhibit calcium dependant ligand binding and a distinctive flattened β-jellyroll structure. C-reactive protein is another acute phase pentraxin. []image CRP[]

SAP belongs to the Ca-dependent legume lectin family and binds binds negatively charged carbohydrates, so it is a heparin- and DNA-binding serum protein.

Human SAP displays 51% sequence homology with CRP, and is more distantly related to the "long" pentraxins such as PTX3 (cytokine modulated) as well as several neuronal pentraxins. CRP and SAP bind to apoptotic and necrotic cells through FcγRFc receptors (FcγRI and/or FcγRIII).[pm] Both SAP and CRP are evolutionarily conserved throughout the vertebrates and are found in distant invertebrates such as the horse-shoe crab (Limulus polyphemus).

SAP prevents fibrillar breakdown by enzymes, so it is considered a factor that maintains the stability of amyloid deposits. Because of its association with amyloid deposits, SAP is considered important in the pathogenesis of systemic amyloidoses. These are conditions characterised by ordered aggregation of normal globular proteins and peptides as insoluble fibres that disrupt tissue architecture and are associated with cell death. Serum amyloid P component (SAP) binds to amyloid fibrils and is a universal constituent of amyloid deposits, including the plaques, amorphous amyloid ß protein deposits and neurofibrillary tangles of Alzheimer disease. When bound to fibrils, SAP prevents proteolysis of the amyloid fibrils of Alzheimer disease, of systemic amyloid A amyloidosis and of systemic monoclonal light chain amyloidosis and may thereby contribute to their persistence [r] SAP is believed to stabilise aggregates by preventing proteolytic cleavage and inhibiting fibril removal via the normal protein scavenging mechanisms.

 Fc receptors  Immune Cytokines  Immunoglobulins

▲§ acute phase ф acute phase inflammatory response : Alzheimer's : amyloid : amyloidoses : AP : autoimmunity ф autoimmunity : complement ф complement system § C-reactive protein § CRP : CRP : cytokines : evolution ф immune cytokines ф immune response : inflammation ф inflammatory response : neurofibrillary tangles : opsonin : pentraxin proteins : plaques : PTX3 : SAP ▲§



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