The B12 anti-tryptase monoclonal antibody disrupts the tetrameric structure of heparin-stabilized beta-tryptase to form monomers that are inactive at neutral pH and active at acidic pH.
The novel tetrameric structure of human beta-tryptase faces each active site into the central pore, thereby restricting access of most biologic protease inhibitors. The mechanism by which the anti-tryptase mAb B12 inhibits human beta-tryptase peptidase and proteolytic activities at neutral pH, but augments proteolytic activity at acidic pH, was examined. At neutral pH, B12-beta-tryptase complexes are inactive. At acidic pH, B12 (intact and Fab) minimally affects peptidase activity when added to beta-tryptase tetramers, but does induce susceptibility to inhibition by soybean trypsin inhibitor and antithrombin III. Surprisingly, B12 Fab-beta-tryptase complexes formed at both neutral and acidic pH exhibit the apparent molecular mass of a complex with 1 beta-tryptase monomer and 1 Fab by gel filtration. B12 does not compete with heparin for binding to tryptase at either neutral or acidic pH. Thus, B12 directly disrupts beta-tryptase tetramers to monomers that are inactive at neutral pH, whereas at acidic pH, are active and more accessible to protein inhibitors and substrates.
Division of Rheumatology, Allergy and Immunology, Department of Internal Medicine, Virginia Commonwealth University, Richmond, VA 23298, USA.
Yoshihiro
Y
Fukuoka
Lawrence B
LB
Schwartz
D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D016264:Dextran Sulfate; D004789:Enzyme Activation / Q000276:immunology; D004795:Enzyme Stability / Q000276:immunology; D005340:Fibrinogen / Q000378:metabolism; D006493:Heparin / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D051379:Mice; D020836:Protein Structure, Quaternary; D012697:Serine Endopeptidases / Q000737:chemistry* / Q000276:immunology* / Q000378:metabolism; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology*; D013552:Swine; D053802:Tryptases
D000911:Antibodies, Monoclonal; D015842:Serine Proteinase Inhibitors; C509190:Tpsb2 protein, mouse; D005340:Fibrinogen; D006493:Heparin; D016264:Dextran Sulfate; D012697:Serine Endopeptidases; C509222:Tpsab1 protein, mouse; D053802:Tryptases