Affinity transfer of nanobodies to a CDR3 only single-domain antibody fragment NBL42 / 国际生物医学工程杂志

ABSTRACT

Objective:To evaluate the potential of a previously identified CDR3 only single-domain antibodies (sdAbs) fragment, NBL42, as a general framework for affinity transfer.Methods:The H3 loops of VHH-A4(A4), VHH-H5(H5), cAb-Lys3(L3) and B6H12 which bind with alliinase, PD-1, lysozyme and CD47, respectively, were grafted into the corresponding loop of NBL42. The genes of the reconstituted CDR3 only sdAbs were synthesized, expressed in E. coliand purified with Ni 2+ column affinity chromatography. The antigen binding and stability of the recombinant CDR3 only sdAbs were assayed by ELISA. Results:The recombinant NBL42-A4CDR3, NBL42-H5CDR3, NBL42-L3CDR3 and NBL42-B6H12CDR3 ran as a single peak at 15, 15, 28 and 16 kDa, respectively, in SDS-PAGE as expected molecular weight. Grafted sdAbs NBL42-A4CDR3 and NBL42-H5CDR3 expressed in a soluble form and specifically bind with alliinase and PD-1, respectively, but lost about 50% of their binding activity. In contrast, the grafted sdAbs NBL42-Lys3CDR3 and NBL42-B6H12CDR3 completely lost their antigen binding capacity. NBL42 sdAbs and grafted sdAbs NBL42-A4CDR3 and NBL42-H5CDR3 retain roughly half of their binding activity after 90 ℃ heat treatment, indicating high stability. The C88Y mutation in NBL42 and the Swiss Mode 3D model predicted that the C88Y residue in FR3 may play a key role in NBL42 stability and CDR3 affinity transfer.Conclusions:The structure of NBL42 has potential as a framework for CDR3 transplantation and affinity transfer.