title: Structure-based affinity maturation of a chimeric anti-ricin antibody C4C13.
abstract: Ricin is a highly lethal toxin. Anti-ricin chimeric monoclonal antibody (mAb) C4C13 was prepared in our lab; however, its binding affinity was much weaker than that of the parent antibody 4C13. In this study, based on the computer-guided homology modeling and conformational optimization methods, the 3-D structure of C4C13 variable regions Fv was constructed and optimized. Using molecular docking and dynamics simulation methods, the 3-D complex structure of ricin and C4C13 Fv was obtained. Considering the orientation property, surface electrostatic distribution, residues chemical and physical character and intermolecular hydrogen bond, the binding mode and key residues were predicted. According to C4C13 Fv fragment and ricin complementary binding surface, electrostatic attraction periphery and van der Waals interaction interface, three mutants (i.e., M1 (N(H102)F, W(H103)Y); M2 (W(H103)Y) and M3 (R(L90)G)) were designed, in which M1 and M2 were predicted to possess higher antigen-binding activity than C4C13, while M3 was weaker. The relative affinity assays by ELISA showed that M1 and M2 mutations had higher affinity (9.6 and 18.3 nmol/L) than C4C13 (130 nmol/L) and M3 had weaker affinity (234.5 nmol/L) than C4C13. The results showed that the modeling complex structure of the antigen (ricin) and antibody (C4C13) is reasonable. Our work offered affinity maturated antibodies by site mutations, which were beneficial for valuable anti-ricin antibody design and preparation in future.
authors.affiliation: a Institute of Basic Medical Sciences , 100850 , Beijing , PR China .
authors.forename: Longlong
authors.initials: L
authors.lastname: Luo
authors.forename: Qun
authors.initials: Q
authors.lastname: Luo
authors.forename: Leiming
authors.initials: L
authors.lastname: Guo
authors.forename: Ming
authors.initials: M
authors.lastname: Lv
authors.forename: Zhou
authors.initials: Z
authors.lastname: Lin
authors.forename: Jing
authors.initials: J
authors.lastname: Geng
authors.forename: Xinying
authors.initials: X
authors.lastname: Li
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.forename: Beifen
authors.initials: B
authors.lastname: Shen
authors.forename: Chunxia
authors.initials: C
authors.lastname: Qiao
authors.forename: Jiannan
authors.initials: J
authors.lastname: Feng
mesh_terms: D000911:Antibodies, Monoclonal / Q000737:chemistry* / Q000235:genetics; D000936:Antigen-Antibody Complex / Q000737:chemistry; D001666:Binding Sites, Antibody; D003198:Computer Simulation; D007135:Immunoglobulin Variable Region / Q000737:chemistry / Q000235:genetics; D062105:Molecular Docking Simulation; D056004:Molecular Dynamics Simulation; D009154:Mutation; D012276:Ricin / Q000737:chemistry* / Q000276:immunology; D013816:Thermodynamics
chemical_list: D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; C526001:C4C13 monoclonal antibody; D007135:Immunoglobulin Variable Region; D012276:Ricin