Thermodynamic stability and functional activity of tumor-associated antibodies.
Tumor-associated antibodies of human IgG1 subclass were eluted from cell-surface antigens of human carcinoma cells and studied by differential scanning calorimetry and binding to local conformational probes, protein A from Staphylococcus aureus and a monoclonal antibody targeted to the CH2 domain of the Fc fragment. At pH 2.0-7.0, we observed virtually identical enthalpies of thermal unfolding for IgG1 from normal human sera and tumor-associated IgG1. The exact values of calorimetric enthalpy (Delta h) at pH 7.0 were 6.1 and 6.2-6.3 cal/g for IgG1 from normal serum and IgG1 from carcinoma cells, respectively. The affinity constants of protein A binding to the CH2--CH3 domain interface demonstrated differences between serum IgG1 and tumor associated IgG1 that did not exceed 3-8-fold. The binding affinity toward the anti-CH2 monoclonal antibody determined for serum IgG1 and IgG1 from carcinoma cells differed not more than 2.5-fold. The thermodynamic parameters of IgG1 from carcinoma cells strongly suggest that protein conformational stability was essentially unaltered and that the Fc fragment of the tumor-derived IgG1 preserved its structural integrity.
St. Petersburg Institute for Nuclear Physics, Russian Academy of Sciences, Gatchina, 188300 Russia. leokon@yahoo.com
O P
OP
Bliznukov
L D
LD
Kozmin
V B
VB
Klimovich
Y I
YI
Tsybovsky
Z I
ZI
Kravchuk
S P
SP
Martsev
D000912:Antibodies, Neoplasm / Q000737:chemistry* / Q000276:immunology* / Q000378:metabolism; D002152:Calorimetry, Differential Scanning; D006801:Humans; D007074:Immunoglobulin G / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013205:Staphylococcal Protein A / Q000378:metabolism; D013816:Thermodynamics; D014407:Tumor Cells, Cultured
D000912:Antibodies, Neoplasm; D007074:Immunoglobulin G; D013205:Staphylococcal Protein A