Structural Determinants of DNA-binding Specificity for Hox Proteins

Hox proteins are a group of homeodomain-containing transcription factors that define the body plan in both vertebrates and invertebrates. Mutations in Hox proteins lead to limb malformations or cancer in humans. Despite having homeodomains with similar sequences and structures, the eight Hox proteins in Drosophila exhibit a variety of DNA-binding specificities when they are in complex with their cofactor Extradenticle (Exd), raising the question of how such diverse specificity is generated. We have identified DNA minor groove shape as a structural determinant for Hox specificity. Using Monte Carlo simulations, we predicted the minor groove widths for Hox-binding sites obtained from a high-throughput experiment - Systematic Evolution of Ligands by Exponential Enrichment with massive parallel sequencing (SELEX-seq). We found that DNA sites selected by anterior Hox proteins have two narrow regions in the minor groove where Hox-Exd binds. In contrast, DNA sites favored by posterior Hox proteins have only one narrow region. Moreover, clustering of Hox proteins based on their preference of DNA minor groove shape reproduced the ordering of Hox genes along the chromosome, suggesting a stri