Amyloid protein SAA is associated with high density lipoprotein from human serum.

Abstract

Human serums contain a protein antigenically related to protein AA, the principal protein of a major class of amyloid substance. The serum antigen, SAA, occurs mainly in a hig molecular weight form, 1 to 2 X 105. This work shows that the bulk of the SAA sediments at density 1.12 g/cm3 and floats at density 1.21 g/cm3, as does the high density lipoprotein HDL3. SAA is associated with the apolipoproteins ApoA-I and ApoA-II. The total cholesterol:total protein ratio of the fraction with density 1.12-1.21 g/cm3 is 0.2:1, consistent with that of HDL3. Acid treatment dissociates a significant portion of the SAA constituent of the HDL3 fraction into low molecular weight species of the order of 13,000. The quantity of SAA may vary from 0.1% up to 1% or more of the total protein of HDL3.Amyloidosis is the term given to a group of diseases characterized by extracellular deposits in various tissues of a material, amyloid substance, now known to be comprised largely of protein. Chemically distinct varieties of amyloid deposits are known (1). Recently most emphasis has been placed upon those cases in which the amyloid substance has a significant complement of immunoglobulin light chain fragments (2). However, the first protein extracted from amyloid substance and recognized as a major constituent of one group of amyloid substance was the polypeptide now called amyloid protein AA (3). This protein was found in the amyloid deposits associated with various chronic inflammatory diseases, such as rheumatoid arthritis, ankylosing spondylitis, chronic osteomeylitis, and tuberculosis in humans. All amyloid deposits of animals so far examined, including monkey, mink, mouse, guinea pig, and duck, yield upon extraction a polypeptide homologous by amino acid sequence with the human protein AA (4-7). Human and monkey protein AA are most nearly alike and consist of 76 amino acid residues, of molecular weights about 8500 and 8620, respectively (8,9). The amino acid sequence of protein AA is not homologous with any known immunoglobulin or with any protein so far identified.Antibodies raised in rabbits against protein AA derived from human amyloid tissue deposits react with a serum constituent called SAA (10-12). The immunoreactive protein SAA has been variously reported to have a molecular weight ranging from 80,000 to 200,000, as estimated by gel chromatography or electrophoresis (10-13). Treatment of serum containing macromolecular SAA with acid causes partial degradation of SAA to a peptide with an estimated molecular weight of about 11 to 15 X 103 (13-15); this protein has an NH2-terminal amino acid sequence identical with that of tissue protein AA (14, 15). It is thought that the low molecular weight peptide is derived from the "native" macromolecular SAA and that the low molecular weight SAA component is the precursor of the protein AA of tissue amyloid deposits.The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordan...

Acid phosphatases bind to the main high density lipoprotein apolipoprotein A‐I

“…Not only is HDL an indicator of the risk of coronary heart disease [16] but it has also been shown to accommodate acute-phase proteins [17] and endotoxins [ 181. Evidence has been reported that HDL are involved in the entry of cholesterol to steroidogenic and hepatic cells [19] and in the net movement of cholesterol out of cells .…”

Expression of Recombinant Feline Serum Amyloid A(SAA) Protein.

“…Human SAA protein contains 104 amino acids, having a molecular mass of 12 kDa [1]. Circulating concentrations of SAA can increase up to 1000-fold within 24-48 hr of an acute stimulus [4] indicating their important protective role, however, no definite function has been demonstrated for SAA protein.…”

The Presence of Two Low Molecular Mass Proteins Immunologically Related to 14 Kilodalton Serum Amyloid A in the Lipoprotein Fraction and Their Decreased Serum Concentrations in Calves with Experimentally Induced Pneumonia

“…Fractions rich in low molecular mass apolipoproteins were next applied to a DEAE-Sephacel (Pharmacia Biotech, Uppsala, Sweden) column (2 × 25 cm), and bound proteins were eluted by use of a linear gradient of NaCl (0-0.125 M, total 1 liter). Fractions containing apoSAA were dialyzed against 10 mM ammonium hydrogen carbonate, using cellulose dialyzer tubing with a 3,500 molecular weight cutoff, after which the dialysate was Serum amyloid A (apoSAA) is an acute phase protein of liver origin and is associated in plasma with the high-density lipoprotein (HDL) fraction [1]. Bovine apoSAA consists of 112 amino acid residues, and its complete sequence has been reported [18].…”