title: Characterization of reconstituted high-density lipoprotein particles formed by lipid interactions with human serum amyloid A.
abstract: The acute-phase human protein serum amyloid A (SAA) is enriched in high-density lipoprotein (HDL) in patients with inflammatory diseases. Compared with normal HDL containing apolipoprotein A-I, which is the principal protein component, characteristics of acute-phase HDL containing SAA remain largely undefined. In the present study, we examined the physicochemical properties of reconstituted HDL (rHDL) particles formed by lipid interactions with SAA. Fluorescence and circular dichroism measurements revealed that although SAA was unstructured at physiological temperature, α-helix formation was induced upon binding to phospholipid vesicles. SAA also formed rHDL particles by solubilizing phospholipid vesicles through mechanisms that are common to other exchangeable apolipoproteins. Dynamic light scattering and nondenaturing gradient gel electrophoresis analyses of rHDL after gel filtration revealed particle sizes of approximately 10nm, and a discoidal shape was verified by transmission electron microscopy. Thermal denaturation experiments indicated that SAA molecules in rHDL retained α-helical conformations at 37°C, but were almost completely denatured around 60°C. Furthermore, trypsin digestion experiments showed that lipid binding rendered SAA molecules resistant to protein degradation. In humans, three major SAA1 isoforms (SAA1.1, 1.3, and 1.5) are known. Although these isoforms have different amino acids at residues 52 and 57, no major differences in physicochemical properties between rHDL particles resulting from lipid interactions with SAA isoforms have been found. The present data provide useful insights into the effects of SAA enrichment on the physicochemical properties of HDL.
authors: Department of Biophysical Chemistry, Kobe Pharmaceutical University, Kobe 658-8558, Japan.
authors: Hiroka
authors: H
authors: Takase
authors: Department of Biophysical Chemistry, Kobe Pharmaceutical University, Kobe 658-8558, Japan.
authors: Hiroki
authors: H
authors: Furuchi
authors: Department of Biophysical Chemistry, Kobe Pharmaceutical University, Kobe 658-8558, Japan. Electronic address: masatnk@kobepharma-u.ac.jp.
authors: Masafumi
authors: M
authors: Tanaka
authors: Department of Clinical and Laboratory Medicine, Jichi Medical University, Tochigi 329-0498, Japan.
authors: Toshiyuki
authors: T
authors: Yamada
authors: Laboratory of Protein Synthesis and Expression, Institute for Protein Research, Osaka University, Suita 565-0871, Japan.
authors: Kyoko
authors: K
authors: Matoba
authors: Laboratory of Protein Synthesis and Expression, Institute for Protein Research, Osaka University, Suita 565-0871, Japan.
authors: Kenji
authors: K
authors: Iwasaki
authors: Laboratory of Protein Organic Chemistry, Institute for Protein Research, Osaka University, Suita 565-0871, Japan.
authors: Toru
authors: T
authors: Kawakami
authors: Department of Biophysical Chemistry, Kobe Pharmaceutical University, Kobe 658-8558, Japan.
authors: Takahiro
authors: T
authors: Mukai
keywords: Apolipoprotein; High-density lipoprotein; Lipid binding; Serum amyloid A