title: Plasmin cleavage of the amyloid beta-protein: alteration of secondary structure and stimulation of tissue plasminogen activator activity.
abstract: Cerebrovascular amyloid beta-protein (A beta) deposition, a key pathological feature of Alzheimer's disease and hereditary cerebral hemorrhage with amyloidosis Dutch-type, can lead to intracerebral hemorrhage; however, the mechanism for this remains unclear. Assembled A beta is a potent stimulator of tissue-type plasminogen activator (tPA) in vitro. Herein, we investigated the stimulation of tPA by freshly solubilized A beta 1-40. The rate of tPA stimulation by A beta 1-40 increased dramatically over time, suggesting that A beta may be altered during the course of the reaction. SDS-PAGE analysis showed that A beta 1-40 was cleaved during the course of the reaction. Subsequent studies showed that it was plasmin, the product of tPA activation of plasminogen, that specifically cleaved A beta 1-40 in the amino terminal region between Arg5 and His6. Plasmin effectively cleaved a chromogenic substrate corresponding to this cleavage site in A beta. Circular dichroism spectral analysis showed that A beta 6-40 adopted a strong beta-sheet secondary structure. This truncated A beta 6-40 peptide was a potent stimulator of tPA in vitro. Our results indicate that beta-sheet secondary structure of A beta, which can be promoted by plasmin cleavage, stimulates tPA activity. These findings suggest that pathologic interactions between A beta, tPA, and plasmin in the cerebral vessel wall could result in excessive proteolysis contributing to intracerebral hemorrhages.
authors.affiliation: Department of Medicine, Health Sciences Center, State University of New York, Stony Brook 11794-8153, USA. wevn@mail.som.sunysb.edu
authors.forename: W E
authors.initials: WE
authors.lastname: Van Nostrand
authors.forename: M
authors.initials: M
authors.lastname: Porter
mesh_terms: D016229:Amyloid beta-Peptides / Q000737:chemistry* / Q000378:metabolism*; D001120:Arginine / Q000378:metabolism; D002942:Circular Dichroism; D004789:Enzyme Activation; D005341:Fibrinolysin / Q000378:metabolism*; D006639:Histidine / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D017433:Protein Structure, Secondary; D010959:Tissue Plasminogen Activator / Q000378:metabolism*
chemical_list: D016229:Amyloid beta-Peptides; D010446:Peptide Fragments; C078592:amyloid beta-protein (1-40); C091513:amyloid beta-protein (6-25); D006639:Histidine; D001120:Arginine; D010959:Tissue Plasminogen Activator; D005341:Fibrinolysin