STRUCTURE OF A HISTIDINE-X(4)-HISTIDINE ZINC-FINGER DOMAIN - INSIGHTSINTO ADR1-UAS1 PROTEIN-DNA RECOGNITION

The solution structure for a mutant zinc finger peptide based on the s equence of the C-terminal ADR1 finger has been determined by two-dimen sional NMR spectroscopy. The mutant peptide, called PAPA, has both pro line residues from the wild-type sequence replaced with alanines. A no nessential cysteine was also replaced with alanine. The behavior of PA PA in solution implicates the prolines in the conformational heterogen eity reported earlier for the wild-type peptide Xu, R. X., Horvath, S . J., & Klevit, R. E. (1991) Biochemistry 30, 3365-3371. The solution structure of PAPA reveals several interesting features of the zinc fi nger motif. The residue immediately following the second cysteine liga nd adopts a positive phi angle, which we propose is a common feature o f this class of zinc fingers, regardless of whether this residue is a glycine. The NMR spectrum and resulting solution structure of PAPA sug gest that a side-chain to side-chain hydrogen bond involving an argini ne and an aspartic acid analogous to one observed in the Zif268 protei n-DNA cocrystal structure exists in solution in the absence of DNA Pa vletich, N. P., and Pabo, C. O. (1991) Science 252, 809-817. A model for the interaction between the two ADR1 zinc fingers and their DNA bi nding sites was built by superpositioning the refined solution structu res of PAPA and ADR1b onto the Zif268 structure. This model offers str uctural explanations for a variety of mutations to the ADR1 zinc finge r domains that have been shown to affect DNA-binding affinity or speci ficity.