To understand how pCW3 is recognized and transferred we have used a combination of structural and genetic studies. We previously determined the crystal structure of the C-terminal domains of the TcpC protein and showed that it had two VirB8-like domains. We now have determined the crystal structure of TcpK, an accessory protein of the relaxosome, in complex with its cognate DNA binding sequence located in the pCW3 origin of transfer (oriT) site (Traore et al., 2018, Nature Communications). Detailed structural information on the coupling protein TcpA, that eluded us for years has now been resolved. The X-ray crystal of TcpA was determined to 2.1 Å by experimental phasing using seleno-methionine labelled protein. The overall fold resembles that of the E. coli chromosome partitioning protein FtsK, although with subtle conformational changes in the motor domain. We also have carried out preliminary Cryo-EM studies of the second conjugative ATPase of pCW3, TcpF.

Altogether, these recent data have advanced our understanding of the mechanism of conjugative DNA transfer in Clostridium perfringens.

Contact : dubouloz@ill.fr