title: Diversification of β-Augmentation Interactions between CDI Toxin/Immunity Proteins.
abstract: Contact-dependent growth inhibition (CDI) is a widespread mechanism of inter-bacterial competition mediated by the CdiB/CdiA family of two-partner secretion proteins. CdiA effectors carry diverse C-terminal toxin domains (CdiA-CT), which are delivered into neighboring target cells to inhibit growth. CDI(+) bacteria also produce CdiI immunity proteins that bind specifically to cognate CdiA-CT toxins and protect the cell from auto-inhibition. Here, we compare the structures of homologous CdiA-CT/CdiI complexes from Escherichia coli EC869 and Yersinia pseudotuberculosis YPIII to explore the evolution of CDI toxin/immunity protein interactions. Both complexes share an unusual β-augmentation interaction, in which the toxin domain extends a β-hairpin into the immunity protein to complete a six-stranded anti-parallel sheet. However, the specific contacts differ substantially between the two complexes. The EC869 β-hairpin interacts mainly through direct H-bond and ion-pair interactions, whereas the YPIII β-hairpin pocket contains more hydrophobic contacts and a network of bridging water molecules. In accord with these differences, we find that each CdiI protein only protects target bacteria from its cognate CdiA-CT toxin. The compact β-hairpin binding pocket within the immunity protein represents a tractable system for the rationale design of small molecules to block CdiA-CT/CdiI complex formation. We synthesized a macrocyclic peptide mimic of the β-hairpin from EC869 toxin and solved its structure in complex with cognate immunity protein. These latter studies suggest that small molecules could potentially be used to disrupt CDI toxin/immunity complexes.
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA 92697, USA.
authors.forename: Robert P
authors.initials: RP
authors.lastname: Morse
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, Santa Barbara, CA 93106-9625, USA.
authors.forename: Julia L E
authors.initials: JL
authors.lastname: Willett
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA 92697, USA.
authors.forename: Parker M
authors.initials: PM
authors.lastname: Johnson
authors.affiliation: Department of Chemistry, University of California, Irvine, Irvine, CA 92697, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Zheng
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA 92697, USA.
authors.forename: Alfredo
authors.initials: A
authors.lastname: Credali
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA 92697, USA.
authors.forename: Angelina
authors.initials: A
authors.lastname: Iniguez
authors.affiliation: Department of Chemistry, University of California, Irvine, Irvine, CA 92697, USA.
authors.forename: James S
authors.initials: JS
authors.lastname: Nowick
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, Santa Barbara, CA 93106-9625, USA; Biomolecular Science and Engineering Program, University of California, Santa Barbara, Santa Barbara, CA 93106-9625, USA.
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Hayes
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA 92697, USA; Department of Pharmaceutical Sciences, University of California, Irvine, Irvine, CA 92697, USA. Electronic address: celia.goulding@uci.edu.
authors.forename: Celia W
authors.initials: CW
authors.lastname: Goulding
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D001427:Bacterial Toxins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D018360:Crystallography, X-Ray; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D025941:Protein Interaction Mapping; D013329:Structure-Activity Relationship; D015011:Yersinia pseudotuberculosis / Q000737:chemistry* / Q000254:growth & development
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; C503242:CdiA protein, E coli; C554743:CdiI protein, E coli; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D046912:Multiprotein Complexes
keywords: DNase; bacterial competition; interspecies growth inhibition; toxin/immunity proteins