Solution Structure of a TBP–TAFII230 Complex Protein Mimicry of the Minor Groove Surface of the TATA Box Unwound by TBP

AbstractGeneral transcription factor TFIID consists of TATA box–binding protein (TBP) and TBP-associated factors (TAFIIs), which together play a central role in both positive and negative regulation of transcription. The N-terminal region of the 230 kDa Drosophila TAFII (dTAFII230) binds directly to TBP and inhibits TBP binding to the TATA box. We report here the solution structure of the complex formed by dTAFII230 N-terminal region (residues 11–77) and TBP. dTAFII23011–77 comprises three α helices and a β hairpin, forming a core that occupies the concave DNA-binding surface of TBP. The TBP-binding surface of dTAFII230 markedly resembles the minor groove surface of the partially unwound TATA box in the TBP–TATA complex. This protein mimicry of the TATA element surface provides the structural basis of the mechanism by which dTAFII230 negatively controls the TATA box–binding activity within the TFIID complex

Fold and function of polypeptide transport-associated domains responsible for delivering unfolded proteins to membranes

Membranes of Gram-negative bacteria, mitochondria and chloroplasts receive and fold β-barrel transmembrane proteins through the action of polypeptide transport-associated (POTRA) domains. In Escherichia coli, folding substrates are inserted into the outer membrane by the essential protein YaeT, a prototypic Omp85 protein. Here, the articulation between tandem POTRA domains in solution is defined by nuclear magnetic resonance (NMR) spectroscopy, indicating an unprecedented juxtaposition. The novel solution orientations of all five POTRA domains are revealed by small-angle X-ray scattering of the entire 46 kDa periplasmic region. NMR titration studies show that strands from YaeT's canonical folding substrate, PhoE, bind non-specifically along alternating sides of its mixed β sheets, thus providing an ideal platform for helping to fold nascent outer-membrane proteins. Together, this provides the first structural model of how multiple POTRA domains recruit substrates from the periplasmic solution into the outer membrane