Figure 1.

Hybrid Ig proteins engineered by shuffling fragments between the two parent proteins, I27 and I32. (A) Sequence alignment of I27 and I32. The secondary structural elements are indicated above the sequences. Residues in block indicate those residues that are identical in both I27 and I32, and residues shaded in gray indicate those that are similar in both parent proteins. (B) Three-dimensional structures of parent proteins as well as the engineered hybrid Ig domains. By interchanging the various secondary structural elements between the two parent proteins, we engineered 13 hybrid proteins. In the hybrid proteins, the fragments coming from parent protein I27 are shown in gray, while those from I32 are shown in black. Left column shows the hybrid daughter proteins whose A′G strands are kept intact during recombination, while the hybrid ones in the right column contain A′G strands from two different parent proteins.