Affinity Improvement of a Humanized Antiviral Antibody by Structure-Based Computational Design

Acquired immune deficiency syndrome (AIDS) is one of the most lethal infectious diseases influencing human community. While fusion of HIV-1 and host cell membranes, viral envelope glycoprotein gp120 is dissociated and a cascade of refolding events is initiated in the viral fusion protein gp41. To promote formation of the co-receptor binding site on the gp120 and initial attachment, HIV-1 employs CD4 as its primary receptor. Ibalizumab, a humanized, anti-CD4 monoclonal antibody for HIV-1 infection, was investigated in silico to design a potential improved antibody. Computer-aided antibody engineering has been successful in the design of new biologics for disease diagnosis and therapeutic interventions. Here, crystal structure of CD4 along with monoclonal antibody Ibalizumab was explored. Thr30, Ser31, Asn52, Tyr53, Asn98 and Tyr99 in heavy chain of Ibalizumab were mutated with 19 standard amino acid residues using computational methods. A set of 720 mutant macromolecules were designed, and binding affinity of these macromolecules to CD4 was evaluated through Ag-Ab docking, binding free-energy calculations, and hydrogen binding estimation. In comparison to Ibalizumab, seven designed theoretical antibody demonstrated better result in all assessments. Therefore, these newly designed macromolecules were proposed as potential antibodies to serve as therapeutic options for HIV infection.