Non-leucine residues in the leucine repeats of Fos and Jun contribute to the stability and determine the specificity of dimerization

Abstract

Various transcription factors, including C/EBP, GCN4 and members of the Fos, Jun and Myc families have been shown to form highly specific complexes via alpha-helical structures referred to as leucine zippers. Experimental evidence has suggested that dimerization involves the formation of hydrophobic bonds between leucine residues in laterally aligned coiled coil structures. However, the specificity of interaction between leucine zipper proteins is not understood. In this study, we show that amino acids, which are located in positions a, e, and g are instrumental in the formation of Fos/Jun heterodimers, presumably by establishing intermolecular electrostatic and hydrophobic interactions. These residues are highly conserved in proteins of the Fos or Jun families but completely different between Fos and Jun, suggesting that these residues determine the specificity of interaction. This conclusion is supported by the observation that the substitution of amino acids in position a or g in Fos with the corresponding Jun amino acids facilitates the association of two Fos leucine repeats. In addition, we show that a conserved histidine residue, located 7 amino acids (i.e., two alpha-helical turns) C-terminally to the 5th leucine in Fos and Jun, is also important for complex formation.

Method for Predicting the State of Association of Discretized Protein Models. Application to Leucine Zippers†

“…Residues at e and g positions seem to be less important. In general, our predictions are in agreement with experiment (Schuermann et al, 1989(Schuermann et al, , 1991O'Shea et al, 1992); however, further investigation is required to determine the specific role of any given residue in the preferential heterodimer formation. Because preferential heterodimer formation results from the relative instability of Fos homodimers, all of the residues responsible for the relative instability of Fos homodimers ultimately drive the process of heterodimerization.…”

“…The Fos-41 sequence corresponds to 41 residues, 160-200, from c-Fos oncoprotein with an additional H200Y mutation (O'Shea et al, 1989;Schuermann et al, 1991). Table 8 presents the fraction of monomeric and dimeric chains at various concentrations for Fos species without the CGG linker.…”

Distinct roles of Jun : Fos and Jun : ATF dimers in oncogenesis

“…Therefore, attempts were made to construct c-Jun and v-Jun proteins that speci®cally bind to DNA as Jun : Fos and Jun : ATF2. For this purpose, the amino acids were mutated that determine the dimerization speci®city of bZip proteins Schuermann et al, 1991; O'Shea et al, 1992; Baxevanis and Vinson, 1993).…”

Oligomerization properties of GCN4 leucine zipper e and g position mutants

“…Dimers with more attractive interactions between oppositely charged residues and fewer repulsive interactions between like charges would be favored over dimers with fewer attractive and more repulsive interactions. The properties of many leucine zipper mutants appear to support this idea (Schuermann et al, 1991;John et al, 1994;Zhou et al, 1994aZhou et al, , 1994b. Indeed, the stability of a set of two-stranded coiled-coil peptides was related linearly to the number of attractive and repulsive interchain and intrachain interactions (Monera et al, 1994).…”

“…Changing the amino acids at the e and g positions can be sufficient to change the dimerization specificity of a leucine zipper (Schuermann et al, 1991;O'Shea et al, 1992O'Shea et al, , 1993Vinson et al, 1993;John et al, 1994;Zhou et al, 1994aZhou et al, , 1994b. Studies on the role of these residues in confemng dimer stability and specificity have focused on their ability to form attractive and repulsive in- terchain ionic interactions.…”