Extending dimerization interfaces: the bZIP basic region can form a coiled coil.

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Abstract
We appended a rationally designed acidic amphipathic protein sequence to the N‐terminus of a leucine zipper. Circular dichroism data indicate that this engineered polypeptide sequence can ‘zipper’ up the basic region of a bZIP monomer into a heterodimeric coiled coil. This propagation of the leucine zipper dimerization interface into the basic region can proceed for up to four heptads and stabilizes the heterodimer complex 2.5 kcal/mol or > 100‐fold. The acidic nature of the extension is the most critical component of the design, suggesting that the extension is acting as a DNA mimetic. The dimerization prevents the basic region in this heterodimeric coiled coil structure from binding to DNA. Gel‐shift, fluorescence and transient transfection assays indicate that the acidic extension appended to a leucine zipper can inactivate the DNA‐binding and transactivation properties of the bZIP protein C/EBP. The three bZIP basic regions examined in this study dimerize with similar stability with the acidic extension, suggesting that this N‐terminal extension can be used to develop dominant‐negatives to other bZIP transcription factors.