Mechanistic insights into how the single point mutation change the autoantibody repertoire

Abstract

A recent study showed that just one point mutation F33 to Y in the H-CDR1 could lead to the autoantibody losing its DNA binding ability. However, the potential molecular mechanisms have not been well elucidated. In this study, we investigated how the antibody lost the DNA binding ability caused by mutation F33 to Y in the H-CDR1. We found that the electrostatic force was not the primary driving force for the interaction between anti-DNA antibodies and the antigen ssDNA, and that the H-CDR2 largely contributed to the binding of antigen ssDNA, even larger than H-CDR1. The H-F33Y mutation could increase the hydrogen-bond interaction but impair the pi-pi stacking interaction between the antibody and ssDNA. We further found that F33_H, W98_H and Y95_L in the wiletype antibody could form the stable pi-pi stacking interaction with the nucleotide bases of ssDNA. However, the Y33 in mutant could not form the parallel sandwich pi-pi stacking interaction with the ssDNA, which could be verified by the result that any functional mutation in three key residues (F33_H, W98_H, and Y95_L) could lead to the loss of ssDNA binding ability of mutant antibody. Our findings may not only deepen the understanding of the underlying interaction mechanism between autoantibody and antigen, but also broad implications in the field of antibody engineer.