Thermodynamic signatures of the antigen binding site of mAb 447-52D targeting the third variable region of HIV-1 gp120.
The third variable region (V3) of HIV-1 gp120 plays a key role in viral entry into host cells; thus, it is a potential target for vaccine design. Human monoclonal antibody (mAb) 447-52D is one of the most broadly and potently neutralizing anti-V3 mAbs. We further characterized the 447-52D epitope by determining a high-resolution crystal structure of the Fab fragment in complex with a cyclic V3 and interrogated the antigen-antibody interaction by a combination of site-specific mutagenesis, isothermal titration calorimetry (ITC) and neutralization assays. We found that 447-52D's neutralization capability is correlated with its binding affinity and at 25 °C the Gibbs free binding energy is composed of a large enthalpic component and a small favorable entropic component. The large enthalpic contribution is due to (i) an extensive hydrogen bond network, (ii) a π-cation sandwiching the V3 crown apex residue Arg(315), and (iii) a salt bridge between the 447-52D heavy chain residue Asp(H95) and Arg(315). Arg(315) is often harbored by clade B viruses; thus, our data explained why 447-52D preferentially neutralizes clade B viruses. Interrogation of the thermodynamic signatures of residues at the antigen binding interface gives key insights into their contributions in the antigen-antibody interaction.
Departments of Biochemistry and Molecular Pharmacology and ‡Department of Pathology, New York University School of Medicine , New York, New York 10016, United States.
April
A
Killikelly
Hui-Tang
HT
Zhang
Brett
B
Spurrier
Constance
C
Williams
Miroslaw K
MK
Gorny
Susan
S
Zolla-Pazner
Xiang-Peng
XP
Kong
D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D000937:Antigen-Antibody Reactions; D001666:Binding Sites, Antibody / Q000276:immunology; D018360:Crystallography, X-Ray; D000939:Epitopes / Q000276:immunology; D015483:HIV Antibodies / Q000276:immunology*; D015699:HIV Envelope Protein gp120 / Q000276:immunology*; D015497:HIV-1 / Q000276:immunology; D006801:Humans; D006860:Hydrogen Bonding; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry / Q000276:immunology*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009500:Neutralization Tests; D013816:Thermodynamics
D000911:Antibodies, Monoclonal; D000939:Epitopes; D015483:HIV Antibodies; D015699:HIV Envelope Protein gp120; D007140:Immunoglobulin Fab Fragments