title: CdiA Effectors Use Modular Receptor-Binding Domains To Recognize Target Bacteria.
abstract: Contact-dependent growth inhibition (CDI) systems encode CdiA effectors, which bind to specific receptors on neighboring bacteria and deliver C-terminal toxin domains to suppress target cell growth. Two classes of CdiA effectors that bind distinct cell surface receptors have been identified, but the molecular basis of receptor specificity is not understood. Alignment of BamA-specific CdiAEC93fromEscherichia coliEC93 and OmpC-specific CdiAEC536fromE. coli536 suggests that the receptor-binding domain resides within a central region that varies between the two effectors. In support of this hypothesis, we find that CdiAEC93fragments containing residues Arg1358 to Phe1646 bind specifically to purified BamA. Moreover, chimeric CdiAEC93that carries the corresponding sequence from CdiAEC536is endowed with OmpC-binding activity, demonstrating that this region dictates receptor specificity. A survey ofE. coliCdiA proteins reveals two additional effector classes, which presumably recognize distinct receptors. Using a genetic approach, we identify the outer membrane nucleoside transporter Tsx as the receptor for a third class of CdiA effectors. Thus, CDI systems exploit multiple outer membrane proteins to identify and engage target cells. These results underscore the modularity of CdiA proteins and suggest that novel effectors can be constructed through genetic recombination to interchange different receptor-binding domains and toxic payloads.IMPORTANCECdiB/CdiA two-partner secretion proteins mediate interbacterial competition through the delivery of polymorphic toxin domains. This process, known as contact-dependent growth inhibition (CDI), requires stable interactions between the CdiA effector protein and specific receptors on the surface of target bacteria. Here, we localize the receptor-binding domain to the central region ofE. coliCdiA. Receptor-binding domains vary between CdiA proteins, andE. colistrains collectively encode at least four distinct effector classes. Further, we show that receptor specificity can be altered by exchanging receptor-binding regions, demonstrating the modularity of this domain. We propose that novel CdiA effectors are naturally generated through genetic recombination to interchange different receptor-binding domains and toxin payloads.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California, USA.
authors.forename: Zachary C
authors.initials: ZC
authors.lastname: Ruhe
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California, USA.
authors.forename: Josephine Y
authors.initials: JY
authors.lastname: Nguyen
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Xiong
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California, USA.
authors.forename: Sanna
authors.initials: S
authors.lastname: Koskiniemi
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California, USA.
authors.forename: Christina M
authors.initials: CM
authors.lastname: Beck
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California, USA.
authors.forename: Basil R
authors.initials: BR
authors.lastname: Perkins
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California, USA.|Biomolecular Science and Engineering Program, University of California, Santa Barbara, Santa Barbara, California, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Low
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California, USA chayes@lifesci.ucsb.edu.|Biomolecular Science and Engineering Program, University of California, Santa Barbara, Santa Barbara, California, USA.
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Hayes
mesh_terms: D000898:Antibiosis; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D001665:Binding Sites; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D018272:Porins / Q000378:metabolism; D011485:Protein Binding; D000072417:Protein Domains; D011991:Receptors, Virus / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; C503914:BamA protein, E coli; C503242:CdiA protein, E coli; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; C113724:OmpC protein; D018272:Porins; D011991:Receptors, Virus; C066743:Tsx protein, E coli
keywords: bacterial competition; cell-cell adhesion; self/nonself discrimination; toxin immunity proteins; type V secretion system