title: Interaction of dipeptydil peptidase IV with amyloid peptides.
abstract: The aggregates of amyloid beta peptides (Aβs) are regarded as one of the main pathological hallmarks of Alzheimer's disease (AD). An imbalance between the rates of synthesis and clearance of Aβs is considered to be a possible cause for the onset of AD. Dipeptidyl peptidases II and IV (DPPII and DPPIV) are serine proteases removing N-terminal dipeptides from polypeptides and proteins with proline or alanine on the penultimate position. Alanine is an N-terminal penultimate residue in Аβs, and we presumed that DPPII and DPPIV could cleave them. The results of present in vitro research demonstrate for the first time the ability of DPPIV to truncate the commercial Aβ40 and Aβ42 peptides, to hinder the fibril formation by them and to participate in the disaggregation of preformed fibrils of these peptides. The increase of absorbance at 334 nm due to complex formation between primary amines with o-phtalaldehyde was used to show cleaving of Aβ40 and Aβ42. The time-dependent increase of the quantity of primary amines during incubation of peptides in the presence of DPPIV suggested their truncation by DPPIV, but not by DPPII. The parameters of the enzymatic breakdown by DPPIV were determined for Aβ40 (Km=37.5 μM, kcat/Km=1.7×10(3)M(-1)sec(-1)) and Aβ42 (Km=138.4 μM, kcat/Km=1.90×10(2)M(-1)sec(-1)). The aggregation-disaggregation of peptides was controlled by visualization on transmission electron microscope and by Thioflavin-T fluorescence on spectrofluorimeter and fluorescent microscope. DPPIV hindered the peptide aggregation/fibrillation during 3-4 days incubation in 20mM phosphate buffer, pH 7.4, 37°C by 50-80%. Ovalbumin, BSA and DPPII did not show this effect. In the presence of DPPIV, the preformed fibrils were disaggregated by 30-40%.
  
  
  CONCLUSIONS
  for the first time it was shown that the Aβ40 and Aβ42 are substrates of DPPIV. DPPIV prohibits the fibrillation of peptides and promotes disaggregation of their preformed aggregates.
authors.affiliation: H. Buniatyan Institute of Biochemistry of Armenian NAS, Yerevan 0014, Armenia. biochem@ipia.sci.am
authors.forename: Svetlana
authors.initials: S
authors.lastname: Sharoyan
authors.forename: Alvard
authors.initials: A
authors.lastname: Antonyan
authors.forename: Sona
authors.initials: S
authors.lastname: Mardanyan
authors.forename: Hayk
authors.initials: H
authors.lastname: Harutyunyan
authors.forename: Naira
authors.initials: N
authors.lastname: Movsisyan
authors.forename: Narek
authors.initials: N
authors.lastname: Hovnanyan
authors.forename: Karlen
authors.initials: K
authors.lastname: Hovnanyan
mesh_terms: D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000737:chemistry / Q000378:metabolism*; D018819:Dipeptidyl Peptidase 4 / Q000378:metabolism*; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D011485:Protein Binding; D059748:Proteolysis
chemical_list: D016229:Amyloid beta-Peptides; D018819:Dipeptidyl Peptidase 4