High-Density Lipoprotein has Different Binding Capacity for Different Apoproteins.

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Abstract
Purified human amyloid protein A (AA) or serum amyloid protein A (SAA) was incubated with normal human high-density lipoprotein (HDL). After ultracentrifugation the amount of AA or SAA associated with HDL was measured. It was found that the binding capacity of HDL for SAA was higher than that for AA. Incubation of these in vitro associated HDL-AA and HDL-SAA complexes with purified apo AI or apo AII resulted in varying degrees of displacement of the associated AA or SAA from HDL. Under the experimental conditions used, apo AI was able to displace AA from HDL, while apo AII was able to displace both SAA and AA. This indicates that the binding capacity of HDL is different for SAA and AA. Mouse acute-phase HDL was isolated and the native complexes were incubated with human apo AII. SAA2, the amyloidogenic SAA variant in mice, was displaced from HDL to a greater extent than SAA1, indicating a lower binding capacity for the amyloidogenic SAA variant for the HDL complexes.