Oligomeric states in sodium ion-dependent regulation of cyanobacterial histidine kinase-2

Iskander M Ibrahim,Jon Nield,John F Allen,Norbert Krauß,Liang Wang,Sujith Puthiyaveetil

doi:10.1007/s00709-017-1196-7

Abstract

Two-component signal transduction systems (TCSs) consist of sensor histidine kinases and response regulators. TCSs mediate adaptation to environmental changes in bacteria, plants, fungi and protists. Histidine kinase 2 (Hik2) is a sensor histidine kinase found in all known cyanobacteria and as chloroplast sensor kinase in eukaryotic algae and plants. Sodium ions have been shown to inhibit the autophosphorylation activity of Hik2 that precedes phosphoryl transfer to response regulators, but the mechanism of inhibition has not been determined. We report on the mechanism of Hik2 activation and inactivation probed by chemical cross-linking and size exclusion chromatography together with direct visualisation of the kinase using negative-stain transmission electron microscopy of single particles. We show that the functional form of Hik2 is a higher-order oligomer such as a hexamer or octamer. Increased NaCl concentration converts the active hexamer into an inactive tetramer. The action of NaCl appears to be confined to the Hik2 kinase domain.

Highlights

Bacteria, algae, plants and fungi adapt to changes in their environments and often utilise a sensor-response circuit known as a two-component signal transduction system (TCS) to elicit physiological responses
The Histidine kinase 2 (Hik2) homologue that is present in almost all cyanobacteria and plants contains a conserved kinase core domain consisting of dimerisation and phosphotransfer (DHp) and catalytic and ATP-binding (CA) together with a GAF sensor domain (Ibrahim et al 2016a; Puthiyaveetil et al 2008)
It has been suggested that membrane-bound and soluble histidine kinases are homodimeric in their functional forms (Bilwes et al 1999; Marina et al 2005; Surette et al 1996) and that some histidine kinases interconvert between an inactive monomer and an active dimer (Surette et al 1996)

Summary

Introduction

Algae, plants and fungi adapt to changes in their environments and often utilise a sensor-response circuit known as a two-component signal transduction system (TCS) to elicit physiological responses. The simplest form of a TCS consists of just two proteins: a conserved sensor histidine kinase (component 1) and a response regulator (component 2) (Fig. 1a). A signal transduction cascade in bacteria usually begins at the cell membrane from where the signal propagates to the cytoplasm through the transmembrane domain of a sensor histidine kinase. Some sensor histidine kinases exist as soluble cytoplasmic or cytosolic proteins that perceive changes within the cell without direct membrane attachment. Functional forms of both membrane-anchored and soluble histidine kinases occur predominantly as homodimers that contain conserved dimerisation and phosphotransfer (DHp) and catalytic and ATP-binding (CA) domains (Fig. 1). The well-characterised membrane-extrinsic, soluble histidine kinases EnvZc (core kinase domain of EnvZ) (Cai et al 2003), VirAc (virulence A) (Pan et al 1993), and CheA (chemotaxis histidine kinase A)

Methods

Results

Conclusion