title: Global shape and ligand binding efficiency of the HIV-1-neutralizing antibodies differ from those of antibodies that cannot neutralize HIV-1.
abstract: Asymmetric disposition of Fab arms in the structures solved for the broadly neutralizing monoclonal antibody (nmAb) IgG1 b12 raised the question of whether the unusual shape observed for b12 is common for all IgG1 mAbs or if there is a difference in the overall shape of nmAbs versus non-nmAbs. We compared small angle x-ray scattering (SAXS) data-based models and limited proteolysis profiles of some IgG1 mAbs known to be having and lacking HIV-1 neutralizing potency. In non-nmAbs, the Fab arms were found to be symmetrically disposed in space relative to central Fc, but in most nmAbs, the Fab arms were asymmetrically disposed, as seen for IgG1 b12. The only exceptions were 2G12 and 4E10, where both Fab arms were closed above Fc, suggesting some Fab-Fc and/or Fab-Fab interaction in the nmAbs that constrained extension of the Fab-Fc linker. Interestingly, these observations were correlated with differential proteolysis profiles of the mAbs by papain. Under conditions when papain could cut both Fab arms of non-nmAbs, only one Fab arm could be removed from neutralizing ones (except for 2G12 and 4E10). Chromatography and small angle x-ray scattering results of papain-digested products revealed that 1) the Fab-Fc or Fab-Fab interactions in unliganded mAbs are retained in digested products, and 2) whereas anti-gp120 non-nmAbs could bind two gp120 molecules, nmAbs could bind only one gp120. Additional experiments showed that except for 2G12 and 4E10, unopen shapes of nmAbs remain uninfluenced by ionic strength but can be reversibly opened by low pH of buffer accompanied by loss of ligand binding ability.
authors.affiliation: From the CSIR-Institute of Microbial Technology, Sector 39-A, Chandigarh 160036, India and.
authors.forename: Ashish K
authors.initials: AK
authors.lastname: Solanki
authors.affiliation: From the CSIR-Institute of Microbial Technology, Sector 39-A, Chandigarh 160036, India and.
authors.forename: Yogendra S
authors.initials: YS
authors.lastname: Rathore
authors.affiliation: From the CSIR-Institute of Microbial Technology, Sector 39-A, Chandigarh 160036, India and.
authors.forename: Maulik D
authors.initials: MD
authors.lastname: Badmalia
authors.affiliation: From the CSIR-Institute of Microbial Technology, Sector 39-A, Chandigarh 160036, India and.
authors.forename: Reema R
authors.initials: RR
authors.lastname: Dhoke
authors.affiliation: From the CSIR-Institute of Microbial Technology, Sector 39-A, Chandigarh 160036, India and.
authors.forename: Samir K
authors.initials: SK
authors.lastname: Nath
authors.affiliation: the Renal Electrolyte Division, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Deepak
authors.initials: D
authors.lastname: Nihalani
authors.affiliation: From the CSIR-Institute of Microbial Technology, Sector 39-A, Chandigarh 160036, India and ashgang@imtech.res.in.
authors.lastname: Ashish
mesh_terms: D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D057134:Antibodies, Neutralizing / Q000737:chemistry* / Q000276:immunology* / Q000378:metabolism; D015497:HIV-1 / Q000276:immunology*; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D008024:Ligands; D008958:Models, Molecular; D010206:Papain / Q000378:metabolism; D011487:Protein Conformation; D059748:Proteolysis
chemical_list: D000911:Antibodies, Monoclonal; D057134:Antibodies, Neutralizing; D007140:Immunoglobulin Fab Fragments; D008024:Ligands; D010206:Papain
keywords: Global Shape; HIV-1 Protease; Limited Proteolysis; Molecular Modeling; Neutralizing Antibodies; Protein Folding; Protein Structure; Small Angle X-ray Scattering; Solution Scattering; X-ray Scattering