serum amyloid P component; 9.5S alpha-1 glycoprotein (SAP)

Introduction

A pentraxin or pentaxin

Function

• major DNA & chromatin-binding protein of plasma
  • may scavenge nuclear material released from damaged circulating cells
• may serve as Ca+2-dependent lectin
  • binds fibronectin, C4-binding protein & glycosaminoglycans
  • binding to all of these ligands is Ca+2-dependent
• SAP is a normal tissue matrix constituent associated with elastic fibers & the glomerular basement membrane.

Structure

• N-glycosylated with a complex biantennary oligosaccharide chain with a sialic acid at the end (disialo-SAP). monosialo- SAP as well as asioalo-SAP are also detected
• circulates as dimer of pentamers
• more than 50% sequence homology with C-reactive protein

Compartment

secreted

Expression

found in serum & urine

Pathology

• SAP binds to all forms of amyloid fibrils & is present in all amyloid desposits including amyloid of basement membrane & amyloid plaques of Alzheimer's disease
• radio-labeled SAP is used as a specific quantitative in vivo tracer for amyloid deposits

Laboratory

• amyloid P component Ag in tissue

More general terms

• acute phase protein
• amyloid
• pentraxin-2 (neuronal pentraxin, NPTX)

Database

• UniProt: http://www.uniprot.org/uniprot/P02743.html
• OMIM: https://mirror.omim.org/entry/104770
• Entrez gene: http://www.ncbi.nlm.nih.gov/sites/entrez?db=gene&cmd=Retrieve&dopt=Graphics&list_uids=325