V-L-V-H DOMAIN ROTATIONS IN ENGINEERED ANTIBODIES - CRYSTAL-STRUCTURES OF THE FAB FRAGMENTS FROM 2 MURINE ANTITUMOR ANTIBODIES AND THEIR ENGINEERED HUMAN CONSTRUCTS

The crystal structures of two pairs of Fab fragments have been determi ned, The pairs comprise both a murine and an engineered human form, ea ch derived from the antitumor antibodies A5B7 and CTM01. Although anti gen specificity is maintained within the pairs, antigen affinity varie s, A comparison of the hypervariable loops for each pair of antibodies shows their structure has been well maintained in grafting, supportin g the canonical loop model. Detailed structural analysis of the bindin g sites and domain arrangements for these antibodies suggests the diff erences in antigen affinity observed are likely to be due to inherent flexibility of the hypervariable loops and movements at the V-L:V-H do main interface. The four structures provide the first opportunity to s tudy in detail the effects of protein engineering on specific antibodi es. (C) 1997 Wiley-Liss, Inc.