ADR1a, a zinc finger peptide, exists in two folded conformations

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Abstract
Two-dimensional NMR (2DNMR) studies of several different zinc finger peptides have yielded a picture of the three-dimensional structure of this small DNA-binding motif. Details of the differences among fingers with different sequences may provide some insight into how these domains interact with DNA. Toward this end, we have reanalyzed the 2DNMR spectra of the C-terminal zinc finger sequence from the yeast transcriptional factor ADR1. Although this was the sequence on which our original report describing the overall fold of zinc fingers was based, complete spectral assignments (reported here) were needed to compare this sequence in detail with that of ADR1b, for which we have reported an atomic level structure. In the process of analyzing the spectra of ADR1a and a mutant of ADR1a, it was noted that the peptides give two sets of NMR lines, indicating that this sequence, unlike the other ADR1 zinc finger sequence, exists in two slowly interconverting folded conformations in solution. Residues that exhibit peak doubling are located in the Cys loop, the alpha-helix, and the extreme C-terminus of the peptide. Differences in NOEs observed for the two forms indicate that there are detectable conformational differences in the Zn2+ cluster and in the fingertip region. This conformational flexibility, which has not been observed for other zinc finger peptides, may stem from the presence of an additional residue between the histidine ligands (His-X4-His versus His-X3-His).