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Containing Phosphotransfer (Hpt) Domain of the Arcb Sensory View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector FEBS 18604 FEBS Letters 408 (1997) 337-340 Interaction between the CheY response regulator and the histidine- containing phosphotransfer (HPt) domain of the ArcB sensory kinase in Escherichia coli Hidenobu Yakua, Masato Katob, Toshio Hakoshimab, Masakatsu Tsuzukia, Takeshi Mizunoa'* "Laboratory of Molecular Microbiology, School of Agriculture, Nagoya University, Chikusa-ku, Nagoya 464, Japan hDepartment of Molecular Biology, Nara Institute of Science and Technology (NAIST), 8916-5 Takayama, Ikoma, Nara 630-01, Japan Received 10 March 1997; revised version received 9 April 1997 Bordetella pertussi BvgS sensory kinase, involved in virulence Abstract Bacteria have devised sophisticated His-Asp phos- phorelay signaling systems for eliciting a variety of adaptive regulation, is another example, which is structurally very sim- responses to their environment. The histidine-containing phos- ilar to ArcB [9,13]. An even more striking instance of such a photransfer (HPt) domain, found in many signal transduction HPt domain has emerged from the yeast Saccharomyces cere- protein, functions as a mediator of the His-Asp phosphorelay. visiae osmoregulatory signaling system [10,14]. The Slnlp- The ArcB anaerobic sensor of E. coli contains such a HPt Ypdlp-Ssklp pathway represents yet another design of the domain, although its function is not fully understood. In this phosphorelay, in which Ypdlp containing a HPt domain study, we provide in vivo and in vitro evidence that the HPt plays a crucial role in the His-Asp phosphorelay. Taking all domain is capable of interacting with the CheY receiver, which these examples together, it was proposed that the HPt do- contains a phospho-accepting aspartate residue. mains in a set of signal transducers function as a novel device © 1997 Federation of European Biochemical Societies. for the signal transduction via multi-step phosphorelay [11]. However, exploration of the structure and function of the HPt Key words: Phosphotransfer signaling in E. coli; domains is still at a very early stage. ArcB anerobic sensor; HPt phosphotransfer domain; CheY response regulator Here we focused our attention on the structure and func- tion of the HPt domain of ArcB (originally named ArcBc; see Fig. 1) [7,8]. We recently determined the 3-dimensional struc- ture of ArcBc by X-ray analysis [15]. Based on this structural 1. Introduction information, to address a relevant issue with regard to the structure and function of the HPt domain, we examined a Adaptive response systems in bacterial cells often involve possible interaction between the HPt domain of ArcB and two components of signal transduction proteins, sensory kin- the well-characterized response regulator, CheY, which is in- ases and response regulators [1-4]. To date, instances of the volved in the signal transduction responsible for the chemo- two-component signaling systems have been described in a taxis in E. coli. large number of bacterial species [5]. Furthermore, some have recently been discovered in eukaryotes, including plas- 2. Materials and methods tids, protozoa, fungi, and plants [6]. Most of these signal transduction proteins contain one of the two common phos- 2.1. Bacteria and plasmids - photransfer signaling domains, transmitter and receiver [5]. E. coli K-12 strain DZ225 (F , AenvZ, AlacU169, araD139, rpsL, relA, thiA,flbB) was constructed previously [16]. This strain carries an The transmitters contain a crucial histidine residue, which is ompC-lacZ fusion gene on the chromosome. Strain CSH26 (A[lac-pro] autophosphorylated in an ATP-dependent manner, whereas ara thi) was also used, which is a wild-type with respect to the chemo- the receivers contain an aspartate residue which can acquire tactic behavior. Plasmids, pIAOOl and pIA005, were constructed pre- a phosphoryl group from the phospho-histidine of the cognate viously [7,8], both of which carry the arcB gene, but the latter has the transmitter. Besides these domains, another common domain mutations resulting in the His-292 to Leu, and Asp-576 to Gin sub- stitutions. has recently been identified, which is also implicated in the phosphotransfer signaling [7-10]. This domain, referred to 2.2. Purification of ArcB1 and CheY here as the histidine-containing phosphotransfer (HPt) do- The ArcBc consisting of the HPt domain was purified as described main contains a crucial histidine residue, which appears to previously [7]. For the purification of CheY, a plasmid was con- function as a mediator of phophorelay by acquiring/transfer- structed in this study, in which the CheY-coding region was placed under the T7-promoter on a versatile overexpression vector (pET- ring a phosphoryl group from/to other components (i.e., His- series, NOVAGEN, USA). From the cells carrying this plasmid, the Asp phosphorelay) [11,12]. CheY protein was purified by essentially the same procedures as those c A typical HPt domain was first discovered in the Esche- described for the purification of AtcB . richia coli ArcB sensory kinase responsible for anaerobic reg- 2.3. Enzyme assays ulation, which is unorthodox in the sense that it contains both ß-Galactosidase activity was determined by Miller's method with a transmitter domain and a receiver domain in its primary slight modifications, as described previously [7]. amino acid sequence (see Fig. 1A) [7,8]. In ArcB, these two typical signaling domains are followed by a HPt domain. The 2.4. Phosphorylation experiment Radioactively phosphorylated ArcBc was prepared and purified as described previously [7,8]. Phosphotransfer experiment with phospho- *Corresponding author. Fax: (81) 52-789-4091 ArcBc and CheY was also carried out as described previously [7,8]. 0014-5793/97/S17.00 © 1997 Federation of European Biochemical Societies. All rights reserved. P//S0014-5793(97)00459-6 338 H. Yaku et al.lFEBS Letters 408 (1997) 337-340 2.5. Chemotactic assay on 'swarm' plates For swarm assays, tryptone semisolid agar (1% tryptone, 0.5% NaCl, 0.3% agar) supplemented with 50 μg/ml ampicillin was used. An aliquot (3 μΐ) of fresh overnight culture in tryptone-glycerol me- dium (1% tryptone, 0.5% NaCl, 0.5% glycerol, and an appropriate cordon and energy source: 0.1 mM glucose or galactose) was spotted onto the semisolid agar plate, which was then incubated at 30°C for 20 h. For swarm assays under the micro-aerobic conditions, the swarm plate was incubated in GasPak Pouch™ (Becton Dickinson Microbiology, USA), at 30°C for 36 h. 3. Results and discussion Fig. 2. An experimental design to examine a possible in vivo inter- action between CheY and the HPt domain of ArcB. The inset data shows ß-galactosidase activities, determined for strain DZ225 carry- We examined a possible interaction between the HPt do- ing each combination of plasmids, as indicated. Details were given main of ArcB and the CheY response regulator, in vivo and in in the text. vitro. The reason we wanted to address this particular issues is following (Fig. 1). The CheY response regulator interacts nor- ArcB might interact with CheY, as in the case of CheA. To mally with the CheA chemotaxis sensor (Fig. IB) [1]. Among gain a new insight into the structure and function of the HPt a number of sensory kinases, the basic structural design of domain, in this study we tested this idea by taking both in CheA is significantly different from that of other orthodox vivo and in vitro approaches. ones (compare with that of the ArcB transmitter domain in Based on the following experimental rationale, an interac- Fig. 1A) [5]. In fact, the short sequence surrounding the phos- tion of CheY and the HPt domain was first assessed in vivo. phorylated histidine site in CheA does not resemble those We previously demonstrated that the HPt domain of ArcB is surrounding the phosphorylation histidine sites of other or- capable of functioning as a phosphodonor in vivo. Here we thodox transmitters (Fig. 1C, compare with that of the ArcB used the previously constructed plasmid (named pIA005), transmitter domain containing His-1 site). Rather, we noticed which specifies a mutant ArcB protein (named ArcB*) con- that the CheA sequence in question is significantly similar to taining His-717, but lacking both His-292 (His to Leu substi- the sequence of His-2 site in the HPt domain (Fig. 1C). Sec- tution) and Asp-576 (Asp to Gin substitution) (Fig. 2). In ond, recent NMR studies revealed that a domain of CheA other words, the mutant ArcB* protein has the functional containing the phosphorylated histidine site (named PI do- HPt domain, but its transmitter and receiver domains are main) has a global fold of five a-helices that contains a presumably inactive. Provided that ArcB* is overexpressed four-helix bundle [17]. On the other hand, the recent X-ray through the multicopy plasmid, it is capable of phosphorylat- analysis of the isolated HPt domain of ArcB revealed that this ing the OmpR response regulator, even in the absence of its domain also consists of six a-helices containing a four-helix cognate EnvZ sensory kinase [7,8]. Consequently, the resul- bundle with a kidney-like shape [15]. Interestingly, an inspec- tant phospho-OmpR activate an ompC-lacZ fusion gene in tion by superpositioning these two structures containing the strain DZ225 (AenvZ), as schematically shown in Fig. 2 active histidine sites of CheA and the HPt domain of ArcB, (note that the ompC gene is one of the targets of the OmpR respectively, suggested that they are significantly similar to transcriptional activator). This particular phenomenon was each other, based on this structural point of view too [15]. used as a hallmark of the in vivo function of the HPt domain These facts led us to envisage the idea that HPt domain of of ArcB, as follows.
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