Conformational Transitions that Enable Histidine Kinase Autophosphorylation and Receptor Array Integration

Area of Science:

• Molecular Biology
• Biochemistry
• Microbiology

Background:

• Bacterial chemotaxis is a crucial process regulated by transmembrane chemoreceptor arrays.
• The histidine kinase CheA plays a central role in signal transduction, with its autophosphorylation activity modulated by receptor stimulation.

Purpose of the Study:

• To elucidate the regulatory mechanisms governing CheA autophosphorylation.
• To understand the role of individual CheA domains (P1-P5) in activity regulation.
• To investigate the structural basis for CheA's response to stimuli.

Main Methods:

• Biochemical assays and X-ray scattering studies on thermostable CheA from Thermotoga maritima.
• Analysis of CheA domain interactions and mobility using non-hydrolyzable ATP analogs.
• Determination of a crystal structure for the dimerization-plus-kinase unit (P3P4).

Main Results:

• The His-containing substrate domain (P1) is sequestered in the inactive state via inter-subunit interactions.
• Non-hydrolyzable ATP analogs release P1, increasing its mobility and autophosphorylation activity.
• The dimerization domain (P3) and linker length are critical for activity and inter-subunit (trans) phosphorylation.

Conclusions:

• CheA's P1 domains are restrained in an off-state by cross-subunit interactions, requiring nucleotide binding for release.
• Structural data reveals interactions supporting a planar CheA conformation essential for membrane array models.
• These findings provide insights into the allosteric regulation of CheA activity during chemotaxis.