Conformational Changes of an Interdomain Linker Mediate Mechanical Signal Transmission in Sensor Kinase BvgS

Abstract

The whooping cough agent, Bordetella pertussis, controls the expression of its large virulence regulon in a coordinated manner through the two-component system BvgAS. BvgS is a dimeric, multidomain sensor kinase. Each monomer comprises, in succession, tandem periplasmic Venus flytrap (VFT) domains, a transmembrane segment, a cytoplasmic Per-Arnt-Sim (PAS) domain, a kinase module, and additional phosphorelay domains. BvgS shifts between kinase and phosphatase modes of activity in response to chemical modulators that modify the clamshell motions of the VFT domains. We have shown previously that this regulation involves a shift between distinct states of conformation and dynamics of the two-helix coiled-coil linker preceding the enzymatic module. In this work, we determined the mechanism of signal transduction across the membrane via a first linker, which connects the VFT and PAS domains of BvgS, using extensive cysteine cross-linking analyses and other approaches. Modulator perception by the periplasmic domains appears to trigger a small, symmetrical motion of the transmembrane segments toward the periplasm, causing rearrangements of the noncanonical cytoplasmic coiled coil that follows. As a consequence, the interface of the PAS domains is modified, which affects the second linker and eventually causes the shift of enzymatic activity. The major features of this first linker are well conserved among BvgS homologs, indicating that the mechanism of signal transduction unveiled here is likely to be generally relevant for this family of sensor kinases.IMPORTANCE Bordetella pertussis produces virulence factors coordinately regulated by the two-component system BvgAS. BvgS is a sensor kinase, and BvgA is a response regulator that activates gene transcription when phosphorylated by BvgS. Sensor kinases homologous to BvgS are also found in other pathogens. Our goal is to decipher the mechanisms of BvgS signaling, since these sensor kinases may represent new targets for antibacterial agents. Signal perception by the sensor domains of BvgS triggers small motions of the helical linker region underneath. The protein domain that follows this linker undergoes a large conformational change that amplifies the initial signal, causing a shift of activity from kinase to phosphatase. Because BvgS homologs harbor similar regions, these signaling mechanisms are likely to apply generally to that family of sensor kinases.

A Novel Bvg-Repressed Promoter Causes vrg -Like Transcription of fim3 but Does Not Result in the Production of Serotype 3 Fimbriae in Bvg − Mode Bordetella pertussis

“…Transcription of bvgR is activated directly by BvgA~P binding to the promoter PbvgR (18). Somewhat atypically compared to other twocomponent sensor kinases, BvgS appears to be turned on, i.e., actively phosphorylating BvgA, in the absence of specific signals, with recent elegant biochemical, structural, and genetic studies supporting this view (19)(20)(21)(22)(23)(24)(25). However, BvgS can be turned off by addition of compounds such as MgSO 4 or nicotinic acid to the growth medium or by culture at lower temperatures (25°C), resulting in the Bvg Ϫ mode, a phenomenon known as modulation (26).…”

Coiled-Coil Antagonism Regulates Activity of Venus Flytrap-Domain-Containing Sensor Kinases of the BvgS Family

“…The PAS domains of BvgS appear to modify their dimeric interface in response to negative modulators. This change in quaternary structure amplifies small changes of conformation and dynamics of upstream linker 1 ( 16 ).…”

“…Linkers 1 and 2 are rather highly conserved in size (see Fig. 1 in reference 16 and Fig. 3 in reference 19 ), while the length of linker X is variable (see Fig.…”

Distinct virulence ranges for infection of mice by Bordetella pertussis revealed by engineering of the sensor-kinase BvgS

“…In BvgS and the majority of its homologs, the transmembrane domain is followed by a two-helix linker called linker 1 that leads to the PAS domain. This is followed by a second two-helix linker, linker 2, that leads to the α-helical Dimerization and Histidine phosphorylation moiety (DHp) of the kinase domain [ 18 , 19 ]. However, a sizeable proportion of BvgS homologs are devoid of a PAS domain and flanking linkers.…”

“…Instead, a two-helix linker called the linker X directly connects the transmembrane segment to the DHp domain [ 20 ]. The two-helix linkers form coiled coils that regulate the BvgS enzymatic activity [ 18 , 19 ]. We have built several chimeras by replacing the region between the TM and DHp domains of BvgS with those from homologs devoid of PAS domain [ 18 , 20 ].…”