Studies on TlpA
The regulator protein of bacterial virulence
Temperature is a primary activator of virulence expression in pathogenic bacteria. Increase in temperature signals entry into a warm blooded host. Though the regulation of many bacterial virulence genes is known in detail, the way by which gene expression becomes activated through temperature changes remains unexplored. There is evidence for the existence of molecular thermometers, suggesting that temperature sensing and gene regulator activity may be combined into a single molecule. A novel type of a sensor regulator has been identified in the pathogenic bacterium Salmonella typhimurium.
Salmonellae are one of the most notorius bacterial agents causing gastro-enterities in humans, and causing serious systematic infections. Virulent isolates of S. dublin and S. typhimurium often posses a virulence plasmid. A conserved region of this plasmid carries the gene tlpA, encoding a protein, TlpA. It has been shown that TlpA is a regulatory protein, and that it has the capacity to modulate its represor activity in response to changes in environmental temperature.
TlpA consists of 371 amino acid residues and forms homo-oligomeric structures in vitro and in vivo. It autoregulates transcription from the tlpA promotor. The primary structure of TlpA can be separated into two functional regions; an N-terminal DNA binding motif, followed by a long helical sensor domain. The evidence for a coiled-coil sensor domain in TlpA is based on a number of observations. The binding to DNA is sequence specific, involving a defined 50 base-pairs recognition sequence.
At low temperature, TlpA is contained in am oligomeric state capable of DNA binding and concominant promotor supression. In crease in temperature may cause a gradual melting of TlpA by shifting the equilibrium towards the monomeric state. As monomeric TlpA is not capable of binding DNA, increasing temperature results in an activation of transcription from the tlpA promotor site.