Vl:vh domain rotations in engineered antibodies: crystal structures of the FAB fragments from two murine antitumor antibodies and their engineered human constructs.
The crystal structures of two pairs of Fab fragments have been determined. The
pairs comprise both a murine and an engineered human form, each derived from the
antitumor antibodies A5B7 and CTM01. Although antigen specificity is maintained
within the pairs, antigen affinity varies. A comparison of the hypervariable
loops for each pair of antibodies shows their structure has been well maintained
in grafting, supporting the canonical loop model. Detailed structural analysis
of the binding sites and domain arrangements for these antibodies suggests the
differences in antigen affinity observed are likely to be due to inherent
flexibility of the hypervariable loops and movements at the VL:VH domain
interface. The four structures provide the first opportunity to study in detail
the effects of protein engineering on specific antibodies.
