Interface switch mediates signal transmission in a two-component system

Abstract

Two-component systems (TCS), which typically consist of a membrane-embedded histidine kinase and a cytoplasmic response regulator, are the dominant signaling proteins for transduction of environmental stimuli into cellular response pathways in prokaryotic cells. HptRSA is a recently identified TCS consisting of the G6P-associated sensor protein (HptA), transmembrane histidine kinase (HptS), and cytoplasmic effector (HptR). HptRSA mediates glucose-6-phosphate (G6P) uptake to supportStaphylococcus aureusgrowth and multiplication within various host cells. How the mechanism by which HptRSA perceives G6P and triggers a downstream response has remained elusive. Here, we solved the HptA structures in apo and G6P-bound states. G6P binding in the cleft between two HptA domains caused a conformational closing movement. The solved structures of HptA in complex with the periplasmic domain of HptS showed that HptA interacts with HptS through both constitutive and switchable interfaces. The G6P-free form of HptA binds to the membrane-distal side of the HptS periplasmic domain (HptSp), resulting in a parallel conformation of the HptSp protomer pair. However, once HptA associates with G6P, its intramolecular domain closure switches the HptA-HptSp contact region into the membrane-proximal domain, which causes rotation and closure of the C termini of each HptSp protomer. Through biochemical and growth assays of HptA and HptS mutant variants, we proposed a distinct mechanism of interface switch-mediated signaling transduction. Our results provide mechanistic insights into bacterial nutrient sensing and expand our understanding of the activation modes by which TCS communicates external signals.

The role of solute binding proteins in signal transduction

“…2 F). These large structural rearrangements caused a tilting of HptS-LBD, leading to a lateral displacement of both transmembrane regions in a manner reminiscent of the other systems studied [30] .…”

“…D) Sensor kinase LuxQ with LuxP [29] (PDB 2HJ9). E,F) Sensor kinase HptS in complex with apo and ligand-loaded HptA [30] (PDB 6LKG, 6LKH). For clarity, only a single monomer of the sensor kinase LBD is shown.…”

“…A crystallographic study of the HptA/HptS-LBD complex has been reported recently [30] . The HptS-LBD belongs to the family of dCache domains that are composed of two α/β modules, generally referred to as membrane distal and membrane proximal module.…”

“…The X-ray study of HptS-LBD in a complex with HptA described above may provide an answer to this question. It was shown that signal-bound HptA links two HptS-LBDs by establishing contacts with the membrane-distal and membrane-proximal modules [30] . Other than the finding that lactate binds to the membrane-proximal module of the TlpC chemoreceptor of H. pylori [67] , this is the first demonstration of a role for the membrane-proximal module of dCache domains in the signaling process.…”

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

“…As outlined above, the range of signals sensed by SHKs is very diverse. A recent example of this diversity and accompanying novel and diverse mechanisms of signal perception is provided by HptS [ 166 ]. HptS is the histidine kinase component of the HptRSA system involved in responses to glucose-6-phosphate in S. aureus .…”