Studying low-density lipoprotein-monoclonal antibody complexes using dynamic laser light scattering and analytical ultracentrifugation

Monoclonal antibody complexes have proven very useful in the study of low-d ensity lipoproteins (LDLs). Thus, complexes composed of two different monoc lonal antibodies, selected from a panel of 11 different antibodies, and LDL have been employed to map apolipoprotein B (apoB) on the surface of the LD L. In this way, apoB was found to surround the LDL as a ribbon with a bow [ Chatterton, J. E., et al. (1995) J. Lipid Res. 36, 2027-2037]. Moreover, mo noclonal MB19, which recognizes a polymorphic site, has been employed to qu antitate the two different allelic forms of apoB found on LDL in human sera , and in this way, we assessed the effect of most of the known common polym orphisms of this protein as well as detected the depletion of the normal al lele product in two forms of familial defective apoB-100 [Chatterton, J, E. , et al. (1995) Biochemistry 34, 9571-9580; Pullinger, C. R., et al. (1995) J. Clin. Invest. 95, 1225-1234]. In this paper, these studies have been ex tended by examining by dynamic light scattering and sedimentation velocity techniques the complexes formed with only one antibody, and complexes forme d using two antibodies. Our data show that the: largest complex formed with a single monoclonal antibody was that of an LDL dimer; no larger, nonspeci fic complexes were present. With two antibodies, a variety of complexes wer e seen. Thus, monoclonal antibodies MB47 and 4G3, which bound about 55 degr ees apart, formed a very stable dimer. Monoclonal antibodies MB47 and 2D8, which bound 136 degrees apart, formed a very stable tetramer, with four LDL s held together in probably a circular structure with four monoclonal antib odies. Finally, monoclonal antibodies 2D8 and 1D1, which bound 86 degrees a part, probably formed a less stable LDL tetramer, held together by three to four monoclonal antibodies. A rationale for these structures is discussed, as well as the biological relevance of these complexes.