Subversion of innate immune responses by Brucella through the targeted degradation of the TLR signaling adapter, MAL

J Immunol. 2010 Jan 15;184(2):956-64. doi: 10.4049/jimmunol.0902008. Epub 2009 Dec 14.


Gram-negative bacteria belonging to the Brucella species cause chronic infections that can result in undulant fever, arthritis, and osteomyelitis in humans. Remarkably, Brucella sp. genomes encode a protein, named TcpB, that bears significant homology with mammalian Toll/IL-1 receptor domains and whose expression causes degradation of the phosphorylated, signal competent form of the adapter MyD88-adapter-like (MAL). This effect of TcpB is mediated through its box 1 region and has no effect on other TLR adapter proteins such as MyD88 or TIR-domain containing adapter protein-inducing IFNbeta. TcpB also does not affect a mutant, signal-incompetent form of MAL that cannot be phosphorylated. Interestingly, the presence of TcpB leads to enhanced polyubiquitination of MAL, which is likely responsible for its accelerated degradation. A Brucella abortus mutant lacking TcpB fails to reduce levels of MAL in infected macrophages. Therefore, TcpB represents a unique pathogen-derived molecule that suppresses host innate-immune responses by specifically targeting an individual adapter molecule in the TLR signaling pathway for degradation.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Brucella / pathogenicity*
  • Cell Line
  • Humans
  • Immunity, Innate*
  • Membrane Glycoproteins / metabolism*
  • Phosphorylation
  • Receptors, Interleukin-1 / metabolism*
  • Sequence Homology, Amino Acid
  • Toll-Like Receptor 4 / metabolism
  • Ubiquitin
  • Viral Proteins / physiology


  • Membrane Glycoproteins
  • Receptors, Interleukin-1
  • TIRAP protein, human
  • TLR4 protein, human
  • Toll-Like Receptor 4
  • Ubiquitin
  • Viral Proteins