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Baseplate Variability of Vibrio Cholerae Chemoreceptor Arrays

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Baseplate Variability of Vibrio Cholerae Chemoreceptor Arrays Baseplate variability of Vibrio cholerae chemoreceptor arrays Wen Yanga,1, Alejandra Alvaradob,1, Timo Glatterc, Simon Ringgaardb,2, and Ariane Briegela,2 aInstitute of Biology, Leiden University, 2333 BE Leiden, The Netherlands; bDepartment of Ecophysiology, Max Plank Institute for Terrestrial Microbiology, 35043 Marburg, Germany; and cCore Facility for Mass Spectrometry and Proteomics, Max Planck Institute for Terrestrial Microbiology, 35043 Marburg, Germany Edited by John S. Parkinson, University of Utah, Salt Lake City, UT, and accepted by Editorial Board Member Caroline S. Harwood November 12, 2018 (received for review July 11, 2018) The chemoreceptor array, a remarkably ordered supramolecular these, clusters I and III are expressed only under certain growth complex, is composed of hexagonally packed trimers of receptor conditions (low oxygen and as a general stress response, respectively) dimers networked by a histidine kinase and one or more coupling (16–18). The proteins from cluster I form cytoplasmic arrays, in proteins. Even though the receptor packing is universal among which two baseplate layers sandwich cytosolic chemoreceptors and chemotactic bacteria and archaea, the array architecture has been are stabilized by a specialized receptor with two signaling domains extensively studied only in selected model organisms. Here, we (19, 20). Cluster III is structurally not well understood at present. show that even in the complete absence of the kinase, the cluster II Neither of these systems has been implicated in canonical che- arrays in Vibrio cholerae retain their native spatial localization and motactic behavior, and their cellular function remains elusive. In the iconic hexagonal packing of the receptors with 12-nm spacing. contrast, cluster II has been shown to be responsible for chemo- Our results demonstrate that the chemotaxis array is versatile in tactic behavior under all tested conditions so far (21). The arrays composition, a property that allows auxiliary chemotaxis proteins formed by cluster II proteins are expressed under standard growth such as ParP and CheV to integrate directly into the assembly. Along conditions as well as under conditions in which clusters I and III with its compositional variability, cluster II arrays exhibit a low de- are also expressed (5, 20). Electron cryotomography (ECT) has gree of structural stability compared with the ultrastable arrays in previously revealed a typical hexagonal packing with a 12-nm spacing in the cluster II arrays (5). The same hexagonal packing Escherichia coli. We propose that the variability in chemoreceptor order was also found in both receptor layers in the cytoplasmic arrays is an important mechanism that enables the incorporation of cluster I arrays (20). V. cholerae possesses 43 MCP genes that are chemotaxis proteins based on their availability. scattered throughout the genome. Thirty-eight of these MCPs belong to the 40-heptad class (22), and this class of receptors in- bacterial chemotaxis | chemoreceptor array | electron cryotomography | tegrates into the cluster II array (23). The cluster II arrays are Vibrio | baseplate strictly localized to the bacterial cell poles by the ParC/ParP sys- tem. ParC acts as a polar determinant that directs localization of hemotactic bacteria constantly assess their environment and arrays to the cell pole via its cognate partner protein, ParP. ParP Ccompare their current situation with that of the recent past integrates into the array via its C-terminal AIF-domain through to bias their movements toward favorable surroundings. Changes interactions with MCPs and CheA. The integration of ParP in their environment are typically detected by transmembrane receptors known as methyl-accepting chemotaxis proteins (MCPs). Significance Nutrients, toxins and biological signaling molecules bind to the periplasmic domains of the receptors either directly or via peri- The chemotaxis array is a macromolecular assembly employed – plasmic binding proteins (1 3). MCPs communicate their binding by motile prokaryotes to sense their chemical environment. state through the membrane to a HAMP domain (present in histi- They share a universal architecture in which trimers of che- dine kinases, adenylyl cyclases, MCPs, and some phosphatases), moreceptor dimers are arranged in a highly conserved hexag- which in turn communicates with their cytoplasmic tips to regulate onal array. However, the cluster II arrays in Vibrio cholerae the autophosphorylation of a histidine kinase, CheA. The kinase exhibit an underappreciated diversity in their composition. transfers phosphoryl (-P) groups to a response regulator, CheY, They have low structural stability despite the retention of the which then diffuses throughout the cell, binds to flagellar motors, canonical receptor packing. Our results demonstrate that che- and regulates their direction of rotation (4). In Escherichia coli, moreceptor arrays have an unexpectedly high variability in either an increase of attractants or a decrease of repellents will composition among species, a property that likely facilitates lead to a reduced CheY-P production. In the presence of low the rapid incorporation of different chemotaxis proteins in CheY-P levels, the flagellar motors rotate counterclockwise, which response to environmental changes. Overall, our results high- results in a smooth-swimming motion (“run”). Increase of CheY-P light the necessity to better understand chemoreceptor arrays promotes a change of spinning direction to clockwise, resulting in and their biological significance outside the model organism. a random reorientation of the cell (“tumbling”). Adjustments in the length of runs cause cells to follow gradients toward attractants Author contributions: W.Y., A.A., S.R., and A.B. designed research; W.Y., A.A., and T.G. and away from repellents. performed research; W.Y., A.A., T.G., S.R., and A.B. analyzed data; and W.Y., A.A., S.R., The arrangement of chemoreceptors in hexagonal arrays has and A.B. wrote the paper. been shown to be universal among organisms in the Bacteria and The authors declare no conflict of interest. Archaea domains (5, 6). In E. coli, the chemoreceptors are net- This article is a PNAS Direct Submission. J.S.P. is a guest editor invited by the Editorial worked by rings of CheA and CheW into hexagonally packed ar- Board. rays with a 12-nm spacing (7–11). Each set of three CheA dimers Published under the PNAS license. that links one receptor hexagon together, lies at the vertices of a 1W.Y. and A.A. contributed equally to this work. larger hexagonal lattice with a spacing of 21 nm (12). This ordered 2To whom correspondence may be addressed. Email: [email protected] or arrangement results in ultrastable receptor arrays that retain their [email protected]. highly ordered architecture, even after cell lysis (8, 12–15). This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. Vibrio cholerae contains three chemotaxis operons (clusters I to 1073/pnas.1811931115/-/DCSupplemental. MICROBIOLOGY III), each of which forms its own structurally distinct arrays. Of Published online December 12, 2018. www.pnas.org/cgi/doi/10.1073/pnas.1811931115 PNAS | December 26, 2018 | vol. 115 | no. 52 | 13365–13370 Downloaded by guest on September 26, 2021 stimulates array formation and prevents the release of chemotaxis function of the array, it is not indispensable for array formation proteins from already-formed arrays (24–26). or the hexagonal packing of chemoreceptors in V. cholerae. The fact that ParP is not part of the chemotaxis system in E. coli reveals a structural variability of the chemotaxis arrays CheA Is Not Necessary for Array Localization. To study the role of among species. Here, we show that that the CheA/CheW-only CheA protein in the localization of cluster II arrays, we analyzed array, as well as the ultrastability of receptor arrays, is charac- array localization in both the wild-type and the triple-cheA- teristic for the chemotaxis system in E. coli, rather than being a deletion strains using a functional YFP-CheW1 fusion (28) as universal feature shared among all chemotactic bacteria and a marker. Ectopic expression and visualization of YFP-CheW1 archaea. We further show that, although the hexagonal packing revealed, as previously described (24, 28), that in wild-type cells, of the chemoreceptors is universal among species, the baseplate YFP-CheW1 localized as distinct clusters at the bacterial cell that binds the receptor tips differs in its composition. Our studies poles in a uni- and bipolar manner (Fig. 2A). Additionally, de- reveal that the baseplate, as a variable structure, allows for the mographic analysis showed that short cells contained a single incorporation of alternative coupling proteins. This feature likely unipolar YFP-CheW1 cluster, whereas longer cells contained a facilitates the exchange of different chemotaxis proteins within bipolar localization of YFP-CheW1 clusters (Fig. 2B). Particu- larly, YFP-CheW1 was unipolarly localized in 53% of cells and existing arrays in response to environmental cues. Our results on bipolarly localized in 44% of cells (Fig. 2C). YFP-CheW1 showed V. cholerae emphasize the importance of understanding the struc- an identical cell length-dependent polar localization pattern in the ture and function of chemoreceptor arrays in nonmodel organisms, triple-cheA-deletion background (Fig. 2 A and B)andasimilarratio especially in organisms in which highly versatile
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