bZIP/bHLH-Hybrid proteins target specific DNA sequences

ORGN 391

Jumi A. Shin, jshin@utm.utoronto.ca, Anna V. Fedorova, afedorov@utm.utoronto.ca, I-San Chan, Adrian Schwartz Mittelman, and Jing Xu, jxu24@utm.utoronto.ca. Department of Chemistry, University of Toronto, Mississauga, ON L5L 1C6, Canada
We hypothesize that we can exploit what Nature has already evolved by manipulating the ?-helix molecular recognition scaffold. We have designed fusion hybrids comprising the basic region/leucine zipper (bZIP) and basic helix-loop-helix (bHLH) motifs: the DNA-binding basic regions from the bHLH have been fused to the leucine zipper dimerization domains from the bZIP. These hybrids are, therefore, bZIP-like in structure, i.e. a pair of ?-helices, dimerized via the leucine zipper coiled coil, that binds specific DNA sequences via the basic regions. We used the basic regions from bHLH proteins Max, AhR, Arnt, and bZIP protein C/EBP, and leucine zippers from bZIP proteins Jun and Fos. Therefore, these proteins can exist as Jun-Fos heterodimers or Jun-Jun homodimers. To our knowledge, this is the first demonstration of hybrids between different protein families that retain structure and DNA-binding function. With these mutant proteins, we expand the DNA-binding repertoire of the bZIP scaffold.