Fusion proteins from artificial and natural structural modules.

The purpose of preparing fusion proteins from designed and natural sequences is mainly twofold; it aims at the stabilization of structure and at the modification of biological activity. Fusion with beta-galactosidase, for example, can increase the intracellular stability and DDT-degrading activity of an artificial DDT-binding peptide, and fusions with a leucine zipper produce mono- and bifunctional single-chain variable domain antibody fragments or homodimeric and heterodimeric DNA-binding proteins like an artificial homodimeric HIV-1 enhancer-binding protein with increased binding specificity and repressor activity. Of importance are also short leader sequences that mediate the translocation of proteins across the cytoplasmic and the nuclear membrane. An interesting by-product of the leucine zipper-mediated dimerization of an HIV-1 enhancer-binding protein was the synthesis and the structural as well as functional characterization of a retro-leucine zipper.