Albumin domain mutants with enhanced Aβ binding capacity identified by phage display analysis for application in various peripheral Aβ elimination approaches of Alzheimer's disease treatment

Deposition of amyloid protein, particularly Abeta1-42 , is a major contributor to the onset of Alzheimer's disease (AD). However, almost no deposition of Abeta in the peripheral tissues could be found. Human serum albumin (HSA), the most abundant protein in the blood, has been reported to inhibit amyloid formation through binding Abeta, which is believed to play an important role in the peripheral clearance of Abeta. We identified the Abeta binding site on HSA and developed HSA mutants with high binding capacities for Abeta using a phage display method. HSA fragment 187-385 (Domain II) was found to exhibit the highest binding capacity for Abeta compared with the other two HSA fragments. To elucidate the sequence that forms the binding site for Abeta on Domain II, a random screening of Domain II display phage biopanning was constructed. A number of mutants with higher Abeta binding capacities than the wild type were identified. These mutants exhibited stronger scavenging abilities than the wild type, as revealed via in vitro equilibrium dialysis of Abeta experiments. These findings provide useful basic data for developing a safer alternative therapy than Abeta vaccines and for application in plasma exchange as well as extracorporeal dialysis.