In this study, published in the journal STRUCTURE, the group of Romé Voulhoux in collaboration with KT Forest group’s (University of Wisconsin, USA) and Loïc Quinton’s group (Liège university Belgium) propose the first experimentally validated three-dimensional structural model of a complete Type 4 Filament.
Using a combination of microbial, biochemical and biophysical techniques including cross-linking mass spectrometry interface identification (CL-MS) we deciphered how the XcpH missing component of the Xcp T2SS pseudopilus architecture plays an adapter function bridging the trimeric initiating tip complex, XcpIJK, with the periplasmic filament of XcpG subunits. In this model, each minor pseudopilin protein caps an XcpG protofilament in an overall pseudopilus compatible with dimensions of the periplasm and the outer membrane-spanning secretin through which substrates pass. Unexpectedly, to fulfill its adapter function, the XcpH N-terminal helix must be unwound, a property shared with XcpG subunits.
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