Regulation of the chemotaxis histidine kinase CheA: A structural perspective

Abstract

Bacteria sense and respond to their environment through a highly conserved assembly of transmembrane chemoreceptors (MCPs), the histidine kinase (CheA), and the coupling protein CheW, hereafter termed "the chemosensory array". In recent years, great strides have been made in understanding the architecture of the underlying chemosensory arrays and how these assemblies engender sensitive and cooperative responses. Nonetheless, a central outstanding question surrounds how receptors modulate the activity of the chemotaxis kinase CheA, the enzymatic output of the sensory system. With a focus on recent advances, we summarize the current understanding of array structure and function to comment on the molecular mechanism by which CheA, receptors and CheW generate the high sensitivity, gain and dynamic range emblematic of bacterial chemotaxis. The complexity of the chemosensory arrays has motivated investigation with many different approaches. In particular, structural methods, genetics, cellular activity assays, nanodisc technology and cryo-electron tomography have provided advances that bridge length scales and connect molecular mechanism to cellular function. Given the high degree of component integration in the chemosensory arrays, we ultimately aim to understand how such networked molecular interactions generate a whole that is truly greater than the sum of its parts.

Engineered chemotaxis core signaling units indicate a constrained kinase-off state

“…Many bacteria employ a complex transmembrane sensory apparatus to modulate their motility in response to the chemical environment (reviewed in (Falke, JJ, et al, 2014;Hazelbauer, GL, et al, 2010;Muok, AR, et al, 2019;Parkinson, JS, et al, 2015). Extensively studied in Escherichia coli (Ec), bacterial chemotaxis relies on transmembrane chemoreceptors to transduce extracellular signals into intracellular phosphorylation events (Falke, JJ, et al, 2014;Hazelbauer, GL, et al, 2010;Muok, AR, et al, 2019;Parkinson, JS, et al, 2015).…”

“…Many bacteria employ a complex transmembrane sensory apparatus to modulate their motility in response to the chemical environment (reviewed in (Falke, JJ, et al, 2014;Hazelbauer, GL, et al, 2010;Muok, AR, et al, 2019;Parkinson, JS, et al, 2015). Extensively studied in Escherichia coli (Ec), bacterial chemotaxis relies on transmembrane chemoreceptors to transduce extracellular signals into intracellular phosphorylation events (Falke, JJ, et al, 2014;Hazelbauer, GL, et al, 2010;Muok, AR, et al, 2019;Parkinson, JS, et al, 2015). The receptors, also known as methyl-accepting chemotaxis proteins (MCPs), organize into a trimer-of-dimers (TOD) that further assemble with the dimeric histidine kinase CheA and coupling protein CheW at their membranedistal tips to produce an extended molecular lattice capable of highly sensitive, cooperative responses (Mello, BA, et al, 2003;Pinas, GE, et al, 2016;Sourjik, V, et al, 2002).…”

“…Despite considerable advances, it remains unclear how CheA is regulated by receptors (Falke, JJ, et al, 2014;Hazelbauer, GL, et al, 2010;Muok, AR, et al, 2019;Parkinson, JS, et al, 2015). CheA is composed of five domains (P1 -P5), each with a distinct function: P1 contains the phosphate-accepting histidine residue, P2 docks CheY, P3 dimerizes the subunits, P4 binds ATP as a member of the GHL family of ATPases, and P5 interacts with CheW to form molecular rings integral to the array architecture.…”

“…X-ray crystallography of composite domains and complexes, cryo-electron-tomography (cryo-ET) of native and ex-vivo assembled arrays, biochemistry, spectroscopic approaches, genetics and MD simulations have been combined to define the architecture and sensing behavior of the arrays (reviewed in (Falke, JJ, et al, 2014;Muok, AR, et al, 2019;Parkinson, JS, et al, 2015)): CheA sits at the interface of two TODs, with the helical P3 domain projecting between them toward the membrane. Paralogous P5 and CheW interact through conserved surfaces at the ends of their b-barrels to form rings composed from two types of interfaces: interface 1, which is proximal to P3 and involves P5 subdomain 1 and CheW subdomain 2; and interface 2, which is distal from P3 and involves P5 subdomain 2 and CheW subdomain 1.…”

“…The ability of receptors to alter Ec CheA phosphotransfer rates by several hundred-fold suggests that the kinase assumes substantially different structural and dynamical states associated with these activity changes (Falke, JJ, et al, 2014;Hazelbauer, GL, et al, 2010;Muok, AR, et al, 2019;Parkinson, JS, et al, 2015). Activity assays with P1 supplied as a separated substrate to the core kinase (domains P3P4P5) in complex with receptors indicate that activation primarily derives from increases in kcat and not changes to the P1 Michaelis constant (KM) (Mello, BA, et al, 2018;Pan, W, et al, 2017).…”