BURIED POLAR RESIDUES AND STRUCTURAL SPECIFICITY IN THE GCN4 LEUCINE-ZIPPER

A conserved asparagine (Asn 16) buried in the interface of the GCN4 le ucine zipper selectively favours the parallel, dimeric, coiled-coil st ructure. To test if other polar residues confer oligomerization specif icity, the structural effects of Gln and Lys substitutions for Asn 16 were characterized. Like the wild-type peptide, the Asn16Lys mutant fo rmed exclusively dimers. In contrast, Gln 16, despite its chemical sim ilarity to Asn, allowed the peptide to form both dimers and trimers. T he Gln 16 side chain was accommodated by qualitatively different inter actions in the dimer and trimer crystal structures. These findings dem onstrate that the structural selectivity of polar residues results not only from the burial of polar atoms, but also depends on the compleme ntarity of the side-chain stereochemistry with the surrounding structu ral environment.