title: Constant domain-regulated antibody catalysis.
abstract: Some antibodies contain variable (V) domain catalytic sites. We report the superior amide and peptide bond-hydrolyzing activity of the same heavy and light chain V domains expressed in the IgM constant domain scaffold compared with the IgG scaffold. The superior catalytic activity of recombinant IgM was evident using two substrates, a small model peptide that is hydrolyzed without involvement of high affinity epitope binding, and HIV gp120, which is recognized specifically by noncovalent means prior to the hydrolytic reaction. The catalytic activity was inhibited by an electrophilic phosphonate diester, consistent with a nucleophilic catalytic mechanism. All 13 monoclonal IgMs tested displayed robust hydrolytic activities varying over a 91-fold range, consistent with expression of the catalytic functions at distinct levels by different V domains. The catalytic activity of polyclonal IgM was superior to polyclonal IgG from the same sera, indicating that on average IgMs express the catalytic function at levels greater than IgGs. The findings indicate a favorable effect of the remote IgM constant domain scaffold on the integrity of the V-domain catalytic site and provide a structural basis for conceiving antibody catalysis as a first line immune function expressed at high levels prior to development of mature IgG class antibodies.
authors.affiliation: Chemical Immunology Research Center, Department of Pathology and Laboratory Medicine, University of Texas Houston Medical School, Houston, Texas 77030, USA.
authors.forename: Gopal
authors.initials: G
authors.lastname: Sapparapu
authors.forename: Stephanie
authors.initials: S
authors.lastname: Planque
authors.forename: Yukie
authors.initials: Y
authors.lastname: Mitsuda
authors.forename: Gary
authors.initials: G
authors.lastname: McLean
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Nishiyama
authors.forename: Sudhir
authors.initials: S
authors.lastname: Paul
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000595:Amino Acid Sequence; D017151:Antibodies, Catalytic / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D000911:Antibodies, Monoclonal / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D020134:Catalytic Domain; D005260:Female; D006801:Humans; D007127:Immunoglobulin Constant Regions / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D007074:Immunoglobulin G / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D007075:Immunoglobulin M / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D007135:Immunoglobulin Variable Region / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data
chemical_list: D017151:Antibodies, Catalytic; D000911:Antibodies, Monoclonal; D007127:Immunoglobulin Constant Regions; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D007135:Immunoglobulin Variable Region