title: Exceptional amyloid beta peptide hydrolyzing activity of nonphysiological immunoglobulin variable domain scaffolds.
abstract: Nucleophilic sites in the paired variable domains of the light and heavy chains (VL and VH domains) of Ig can catalyze peptide bond hydrolysis. Amyloid beta (Abeta)-binding Igs are under consideration for immunotherapy of Alzheimer disease. We searched for Abeta-hydrolyzing human IgV domains (IgVs) in a library containing a majority of single chain Fv clones mimicking physiological VL-VH-combining sites and minority IgV populations with nonphysiological structures generated by cloning errors. Random screening and covalent selection of phage-displayed IgVs with an electrophilic Abeta analog identified rare IgVs that hydrolyzed Abeta mainly at His14-Gln15. Inhibition of IgV catalysis and irreversible binding by an electrophilic hapten suggested a nucleophilic catalytic mechanism. Structural analysis indicated that the catalytic IgVs are nonphysiological structures, a two domain heterodimeric VL (IgVL2-t) and single domain VL clones with aberrant polypeptide tags (IgVL-t'). The IgVs hydrolyzed Abeta at rates superior to naturally occurring Igs by 3-4 orders of magnitude. Forced pairing of the single domain VL with VH or VL domains resulted in reduced Abeta hydrolysis, suggesting catalysis by the unpaired VL domain.Angstrom level amino acid displacements evident in molecular models of the two domain and unpaired VL domain clones explain alterations of catalytic activity. In view of their superior catalytic activity, the VL domain IgVs may help attain clearance of medically important antigens more efficiently than natural Igs.
authors.affiliation: Chemical Immunology Research Center, Department of Pathology and Laboratory Medicine, University of Texas Houston Medical School, Houston, Texas 77030, USA.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Taguchi
authors.forename: Stephanie
authors.initials: S
authors.lastname: Planque
authors.forename: Gopal
authors.initials: G
authors.lastname: Sapparapu
authors.forename: Stephane
authors.initials: S
authors.lastname: Boivin
authors.forename: Mariko
authors.initials: M
authors.lastname: Hara
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Nishiyama
authors.forename: Sudhir
authors.initials: S
authors.lastname: Paul
mesh_terms: D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000737:chemistry*; D002384:Catalysis; D019281:Dimerization; D006801:Humans; D006868:Hydrolysis; D007135:Immunoglobulin Variable Region / Q000737:chemistry*; D007700:Kinetics; D008956:Models, Chemical; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary
chemical_list: D016229:Amyloid beta-Peptides; D007135:Immunoglobulin Variable Region; D010455:Peptides