ALTERNATING ZINC FINGERS IN THE HUMAN MALE-ASSOCIATED PROTEIN ZFY - HX3H AND HX4H MOTIFS ENCODE A LOCAL STRUCTURAL SWITCH

The two-finger repeat in the human male-associated protein ZFY provides a model for comparative 2D-NMR studies of classical and variant Zn fingers. This repeat is defined in part by an alternation in spacing between consensus (HX3H) and variant (HX4H) histidine spacings. To investigate the effects of a "switch" between alternative histidine spacings, we have designed an HX3H analogue of a representative HX4H domain of known structure [ZFY-6; Kochoyan, M., Havel, T., Nguyen, D. T., Dahl, C. E., Keutmann, H. T., & Weiss, M. A. (1991) Biochemistry 30, 3371-3386]. The HX3H analogue (designated ZFY-switch) forms a tetrahedral Co2+ complex whose thermodynamic stability is similar to that of the parent peptide. 2D-NMR studies demonstrate that ZFY-switch and ZFY-6, although similar in overall structure, exhibit significant local changes near the site of deletion. Whereas the HX4H site in the native finger forms a nonstandard loop, the HX3H site in ZFY-switch folds as a 3(10) extension of the C-terminal alpha-helix, as observed in the NMR solution structure of a consensus HX3H domain [Lee, M. S., Gippert, G. P., Soman, K. V., Case, D. A., & Wright, P. E. (1989) Science 245, 635-637] and in the crystal structure of a representative Zn finger-DNA complex [Pavletich, N. P., & Pabo, C. O. (1991) Science 252, 809-817]. We propose that variant histidine spacings (HX3H and HX4H) encode a local switch between alternative surface architectures with implications for models of protein-DNA recognition.