STRUCTURAL-ANALYSIS OF THE PURINE REPRESSOR, AN ESCHERICHIA-COLI DNA-BINDING PROTEIN

The purine repressor protein, PurR, is a member the lac repressor, Lac I, family of Escherichia coli DNA-binding proteins that bind DNA via a highly conserved N-terminal helix-turn-helix motif. Additionally, the members of this family display strong sequence homologies between the ir larger C-terminal effector binding/oligomerization domains. Analysi s of the PurR primary and secondary structures reveals that its C-term inal corepressor binding domain is highly homologous to another group of E. coli-binding proteins, the periplasmic binding proteins, particu larly to the ribose-binding protein (RBP). The high resolution x-ray s tructure of RBP allows this protein to serve as a template with which to model the predicted secondary structure of the corepressor binding domain of PurR. Similarly, the N-terminal DNA binding domain of PurR c an be modeled using the NMR-determined structure of the corresponding region (residues 1-56) from LacI as a template. Combining the two, res ults in a description of the likely secondary structure topology of Pu rR and implicates residues important for corepressor binding and dimer ization. CD spectroscopic studies on PurR, its corepressor binding dom ain and RBP result in secondary structure estimates nearly identical w ith those obtained by sequence analyses, thereby providing further cor roborating physical evidence for this topological assignment.