Laminin interactions with the apoproteins of acute-phase HDL: preliminary mapping of the laminin binding site on serum amyloid A.
During AA amyloidosis, the major basement membrane components, collagen type-IV (C-IV), entactin, laminin and perlecan codeposit both spatially and temporally with AA fibrils. Our previous work demonstrated that laminin, and collagen type-IV, can associate with high affinity to a mixture of mouse acute-phase serum amyloid A isoforms (apoSAA1, apoSAA2 and apoSAA3). However, laminin also bound to residual HDL from which apoSAAs were extracted. To characterize further laminin binding specificity for acute-phase HDL apolipoproteins, we have systematically isolated the acute-phase apoSAAs, apoA-I, apoA-II and the apoCs (I, II and III) by reverse phase high pressure liquid chromatography (RP-HPLC), and tested their laminin binding activities individually by ELISA. All the apoSAAs tested bound laminin saturably and with high affinity (Kd approximately 2 nM). In addition, apoA-I also showed laminin binding activity (Kd approximately 4.6 nM). Specific binding for apoA-II and the apo-Cs was not detected. To localize the laminin binding site on apoSAA, we generated defined CNBr fragments of apoSAA1 and apoSAA2, purified them by RP-HPLC, and tested their laminin binding activity by ELISA. A 53 residue peptide corresponding to residues 24-76 of apoSAA2 had the highest laminin binding activity, followed by an 80 residue peptide corresponding to residues 24-103 of apoSAA1, both of which contain a 30 residue sequence that has changed little during evolution. In addition, a 7 residue peptide (residues 17-23), which is common to both apoSAA1 and apoSAA2, also had laminin binding activity. We postulate that laminin facilitates AA amyloidogenesis by sequestering apoSAA and providing a "surface" on which heparan sulfate-dependent fibrillogenic nucleation events can take place.
Ancsin
J B
JB
Department of Pathology, Queen's University, Kingston, Ontario, Canada.
Kisilevsky
R
R
D000209:Acute-Phase Proteins / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001053:Apolipoproteins / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D005260:Female; D007797:Laminin / Q000378:metabolism*; D008075:Lipoproteins, HDL / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D000685:Serum Amyloid A Protein / Q000737:chemistry / Q000378:metabolism*
D000209:Acute-Phase Proteins; D001053:Apolipoproteins; D007797:Laminin; D008075:Lipoproteins, HDL; D020033:Protein Isoforms; D000685:Serum Amyloid A Protein