title: A Localized Complex of Two Protein Oligomers Controls the Orientation of Cell Polarity.
abstract: Signaling hubs at bacterial cell poles establish cell polarity in the absence of membrane-bound compartments. In the asymmetrically dividing bacteriumCaulobacter crescentus, cell polarity stems from the cell cycle-regulated localization and turnover of signaling protein complexes in these hubs, and yet the mechanisms that establish the identity of the two cell poles have not been established. Here, we recapitulate the tripartite assembly of a cell fate signaling complex that forms during the G1-S transition. Usingin vivoandin vitroanalyses of dynamic polar protein complex formation, we show that a polymeric cell polarity protein, SpmX, serves as a direct bridge between the PopZ polymeric network and the cell fate-directing DivJ histidine kinase. We demonstrate the direct binding between these three proteins and show that a polar microdomain spontaneously assembles when the three proteins are coexpressed heterologously in anEscherichia colitest system. The relative copy numbers of these proteins are essential for complex formation, as overexpression of SpmX inCaulobacterreorganizes the polarity of the cell, generating ectopic cell poles containing PopZ and DivJ. Hierarchical formation of higher-order SpmX oligomers nucleates new PopZ microdomain assemblies at the incipient lateral cell poles, driving localized outgrowth. By comparison to self-assembling protein networks and polar cell growth mechanisms in other bacterial species, we suggest that the cooligomeric PopZ-SpmX protein complex inCaulobacterillustrates a paradigm for coupling cell cycle progression to the controlled geometry of cell pole establishment.IMPORTANCELacking internal membrane-bound compartments, bacteria achieve subcellular organization by establishing self-assembling protein-based microdomains. The asymmetrically dividing bacteriumCaulobacter crescentususes one such microdomain to link cell cycle progression to morphogenesis, but the mechanism for the generation of this microdomain has remained unclear. Here, we demonstrate that the ordered assembly of this microdomain occurs via the polymeric network protein PopZ directly recruiting the polarity factor SpmX, which then recruits the histidine kinase DivJ to the developing cell pole. Further, we find that overexpression of the bridge protein SpmX inCaulobacterdisrupts this ordered assembly, generating ectopic cell poles containing both PopZ and DivJ. Together, PopZ and SpmX assemble into a cooligomeric network that forms the basis for a polar microdomain that coordinates bacterial cell polarity.
authors.affiliation: Department of Developmental Biology, Stanford University School of Medicine, Stanford, California, USA.|Department of Biology, Stanford University, Stanford, California, USA.
authors.forename: Adam M
authors.identifier: 0000-0002-2300-9855
authors.initials: AM
authors.lastname: Perez
authors.affiliation: Department of Developmental Biology, Stanford University School of Medicine, Stanford, California, USA.|Department of Biochemistry, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Thomas H
authors.identifier: 0000-0002-3821-1466
authors.initials: TH
authors.lastname: Mann
authors.affiliation: Department of Developmental Biology, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Keren
authors.initials: K
authors.lastname: Lasker
authors.affiliation: Department of Developmental Biology, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Ahrens
authors.affiliation: Stanford Protein and Nucleic Acid Facility, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Eckart
authors.affiliation: Department of Developmental Biology, Stanford University School of Medicine, Stanford, California, USA shapiro@stanford.edu.
authors.forename: Lucy
authors.initials: L
authors.lastname: Shapiro
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D016935:Caulobacter crescentus / Q000166:cytology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D002455:Cell Division; D016764:Cell Polarity; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D011485:Protein Binding; D055503:Protein Multimerization; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D011994:Recombinant Proteins