Structural studies of T4S systems by electron microscopy

Abstract: Type IV secretion (T4S) systems are large dynamic nanomachines that transport DNA and/or proteins through the membranes of bacteria. Analysis of T4S system architecture is an extremely challenging task taking into account their multi protein organisation and lack of overall global symmetry. Nonetheless the last decade demonstrated an amazing progress achieved by X-ray crystallography and cryo-electron microscopy. In this review we present a structural analysis of this dynamic complex based on recent advances in biochemical, biophysical and structural studies

THAP proteins target specific DNA sites through bipartite recognition of adjacent major and minor grooves

THAP-family C(2)CH zinc-coordinating DNA-binding proteins function in diverse eukaryotic cellular processes, such as transposition, transcriptional repression, stem-cell pluripotency, angiogenesis and neurological function. To determine the molecular basis for sequence-specific DNA recognition by THAP proteins, we solved the crystal structure of the Drosophila melanogaster P element transposase THAP domain (DmTHAP) complexed with a natural 10-base pair site. In contrast to C(2)H(2) zinc fingers, DmTHAP docks a conserved β-sheet into the major groove and a basic C-terminal loop into the adjacent minor groove. We confirmed specific protein-DNA interactions by mutagenesis and DNA binding assays. Sequence analysis of natural and in-vitro-selected binding sites suggests several THAPs (DmTHAP, human THAP1 and THAP9) recognize a bipartite TxxGGGx(A/T) consensus motif; homology suggests THAP proteins bind DNA through a bipartite interaction. These findings reveal the conserved mechanisms by which THAP-family proteins engage specific chromosomal target elements