Saturday, May 28, 2011

Autoinhibitory regulation of TrwK, an essential VirB4 ATPase in type IV secretion systems

Alejandro Peña, Jorge Ripoll-Rozada, Sandra Zunzunegui, Elena Cabezón, Fernando de la Cruz & Ignacio Arechaga.
Intergenomics Group. Universidad de Cantabria and Instituto de Biomedicina y Biotecnologia de Cantabria (IBBTEC), Spain

Abstract

Type IV secretion systems (T4SS) mediate the transfer of DNA and protein substrates to target cells. TrwK, encoded by the conjugative plasmid R388, is a member of the VirB4 family, comprising the largest and most conserved proteins of T4SS. In a previous work we demonstrated that TrwK is able to hydrolyze ATP. Here, based on the structural homology of VirB4 proteins with the DNA-pumping ATPase TrwB coupling protein, we generated a series of variants of TrwK where fragments of the C-terminal domain were sequentially truncated. Surprisingly, the in vitro ATPase activity of these TrwK variants was much higher than that of the wild type enzyme. Moreover, addition of a synthetic peptide containing the amino acid residues comprising this C-terminal region resulted in the specific inhibition of the TrwK variants lacking such domain. These results indicate that the C-terminal end of TrwK plays an important regulatory role in the functioning of the T4SS.