Structural Basis of Signal Transduction and Specificity in Two-components Systems
Patricia Casino, Marisa López-Redondo and Alberto Marina
from: Two-Component Systems in Bacteria (Edited by: Roy Gross and Dagmar Beier). Caister Academic Press, U.K. (2012)
Two-component systems (TCSs) constitute a signal transduction mechanism, mainly found in prokaryotes, which is relatively simple as they are basically formed by two proteins: a histidine kinase (HK) and a response regulator (RR). These two proteins are able to transmit all kinds of signals productively and elegantly by the use of phosphorelays in order to ensure cell survival. For this purpose, the HK possesses many qualities; first it is able to sense a signal, second it binds ATP, and third it autophosphorylates on a catalytic His residue. Subsequently, the RR comes into play to promote the final response, but first it needs to be phosphorylated on a catalytic Asp residue via a phosphoryl group transfer from the phosphorylated His of the HK. The phosphorylated RR (RR~P) can thus elicit many diverse responses, which generally involve binding to DNA to activate specific genes. Finally, the system is shut down by the dephosphorylation of the RR~P, a mechanism which can be performed by the RR itself, or assisted by the HK. Undoubtedly, understanding the molecular basis of specificity in the interaction between HK and RR couples as well as the complete catalytic mechanism between these two molecules in the signaling process is especially important from many viewpoints, including the medical, and recent advances in the structural and biochemical field have contributed decidedly read more ...