Membrane Sensor Histidine Kinases: Insights from Structural, Ligand and Inhibitor Studies of Full-Length Proteins and Signalling Domains for Antibiotic Discovery

Abstract

There is an urgent need to find new antibacterial agents to combat bacterial infections, including agents that inhibit novel, hitherto unexploited targets in bacterial cells. Amongst novel targets are two-component signal transduction systems (TCSs) which are the main mechanism by which bacteria sense and respond to environmental changes. TCSs typically comprise a membrane-embedded sensory protein (the sensor histidine kinase, SHK) and a partner response regulator protein. Amongst promising targets within SHKs are those involved in environmental signal detection (useful for targeting specific SHKs) and the common themes of signal transmission across the membrane and propagation to catalytic domains (for targeting multiple SHKs). However, the nature of environmental signals for the vast majority of SHKs is still lacking, and there is a paucity of structural information based on full-length membrane-bound SHKs with and without ligand. Reasons for this lack of knowledge lie in the technical challenges associated with investigations of these relatively hydrophobic membrane proteins and the inherent flexibility of these multidomain proteins that reduces the chances of successful crystallisation for structural determination by X-ray crystallography. However, in recent years there has been an explosion of information published on (a) methodology for producing active forms of full-length detergent-, liposome- and nanodisc-solubilised membrane SHKs and their use in structural studies and identification of signalling ligands and inhibitors; and (b) mechanisms of signal sensing and transduction across the membrane obtained using sensory and transmembrane domains in isolation, which reveal some commonalities as well as unique features. Here we review the most recent advances in these areas and highlight those of potential use in future strategies for antibiotic discovery. This Review is part of a Special Issue entitled “Interactions of Bacterial Molecules with Their Ligands and Other Chemical Agents” edited by Mary K. Phillips-Jones.

Two-Component Systems of S. aureus: Signaling and Sensing Mechanisms

“…Such blockers are thought to be less prone to the development of resistance because bacterial growth is usually not inhibited. Non-native small molecules and peptides capable of interfering with TCSs have been analyzed and have shown significant value as research tools and as potential antivirulence agents [ 146 ]. “Quorum quenchers” (inhibitors of quorum sensing) are of special interest and have been shown to block S. aureus virulence in animal models [ 115 , 147 , 148 , 149 ].…”

Analytical Ultracentrifugation as a Matrix-Free Probe for the Study of Kinase Related Cellular and Bacterial Membrane Proteins and Glycans

“…It is hoped that this short but targeted review has provided a snapshot of the usefulness of the analytical ultracentrifuge for the study of membrane associated proteins and glycans associated with kinase activity, adding to the powerful array of techniques now available and covered in recent reviews by Phillips-Jones and colleagues [ 52 , 56 ]. We have focused on two examples—one for a membrane protein/glycan from a human cellular system—the band 3 protein which has been fully studied in aqueous and detergent systems reflecting the cytoplasmic and transmembrane domains, respectively.…”

“…Not only are these analytical ultracentrifuge methods particularly useful because they do not require separation media, columns or membranes or immobilisation onto a surface, they can in addition form a seminal part of a powerful array of biophysical techniques as we have seen for the vancomycin-mucin systems. Although perhaps insufficiently considered in the past the analytical ultracentrifuge would appear to have an important role to play in the battle against important kinase related diseases and in our understanding of the factors that underpin antimicrobial resistance [ 52 , 57 ].…”

“…The extensive work on band 3 provides the basis for comparison for a current ongoing hydrodynamic study on the enterococcal VanS kinase membrane protein (of monomer molecular mass M 1 ~47 kDa) and its interaction with the aqueous soluble antibiotic glycan vancomycin (M 1 = 1449 Da) [ 3 , 4 , 5 ]. The importance of the enterococcal VanS kinase system and relevance to antimicrobial resistance has been considered elsewhere in this volume by Ma and Phillips-Jones [ 52 ]. Our focus has been on the hydrodynamic properties of the VanS system in the presence and absence of vancomycin, as well as the self-associative properties of vancomycin and its complexation with mucin glycoproteins of relevance to the oral administration of this drug which is mainly administered intravenously.…”

Diversity in Sensing and Signaling of Bacterial Sensor Histidine Kinases

“…The in vitro study was performed using a truncated cytoplasmic region of EvgS, and the results of in vitro studies may not necessarily reflect the actual cell response. Emphasis on employing fulllength HKs in in vitro studies has been recently reviewed [156]. Although the molecular mechanism of how ubiquinone and ubiquinol control EvgS remains unclear, this may be an example of the integration of two signals in the PAS domain [134].…”