Effect of disruption of 3D8 complementarity-determining regions on properties of 3D8 antibody

Abstract

Modifications such as substitution, insertion, or deletion of amino acids within or near CDRs (complementarity-determining regions) in antibodies have been utilized to improve antigen-binding affinity and/or stability. However, little is reported about functional consequence by the disruption of whole amino acid sequence in CDRs of an antibody with multiple activities. Here, we dissected influence of each whole CDR-disruption on the function of an antibody, 3D8 scFv (single chain variable fragment; variable region of heavy chain connected to variable region of light chain by (G4S1)3 linker) which has DNA-binding/-hydrolyzing, heparin-binding and cell-penetrating activities. We generated single CDR-disrupted antibodies in the formats of scFv (sc-H/LCDRi; inactivated-CDR of variable domain of heavy or light chain in scFv format), VH (H-CDRi; inactivated-CDR of variable domain of heavy chain single domain format), and VL (L-CDRi; inactivated-CDR of variable domain of light chain single domain format) by replacing the amino acid sequence of each CDRs with (GlySer)n of same length. DNA-binding activity of sc-variants except sc-L1i was similar to 3D8 scFv, and VH variants had higher affinity to DNA than VH wild type. Therefore, L-CDR1 in 3D8 scFv format is likely to be responsible for DNA-binding activity. Sc-H3i and sc-L3i still retained the heparin-binding activity similar to 3D8 scFv. Moreover, sc-H3i, sc-L3i and H-3i entered the HeLa cells and localized in cytosol of the HeLa cells like 3D8 scFv. It seems that at least H-CDR3 and L-CDR3 in 3D8 scFv format contribute to interaction with heparin and penetration the HeLa cells. For DNA-hydrolyzing activity, sc-L1i, sc-L3i, 3D8 VH and VH’s variants did not hydrolyze DNA. Thus L-CDR1 and L-CDR3 in 3D8 scFv format is not related with hydrolysis of DNA. Next, we examined which CDRs are responsible for the activities of 3D8 antibody using synthesized peptides corresponding to 3D8-CDRs. Only pep-L1 bound to DNA or heparin, however pep-L1 did not enter the HeLa cells. Pep-H1 and pep-H2 entered the HeLa cells, even though much lower penetration efficiency than Tat peptide. Consequently, our results show that effect of the single CDR-disruptions on activities of 3D8 antibody is different between scFv format and single domain format. Only L-CDR1 of 3D8 scFv is important region for DNA-binding/hydrolyzing and cell-penetrating activities.