id="title" class="nomar"Structure-Function Analysis of Polymorphic CDI Toxin-Immunity Protein Complexes
This biological project is composed of investigators from UC Irvine and UC Santa Barbara, and is partnered with the PSI High-Throughput Structure Determination center MCSG.
Bacteria have evolved complex strategies to compete and communicate with one another. A new mechanism of interbacterial competition, termed contact-dependent growth inhibition (CDI) was recently discovered in Escherichia coli. CDI systems are found in a wide variety of gram-negative bacteria, including many important human pathogens. CDI is mediated by the CdiB/CdiA two-partner secretion system. CdiB is a predicted outer membrane protein that is required for the export and assembly of the CdiA exoprotein onto the cell surface. The C-terminal region of CdiA (CdiA-CT) contains the growth inhibition activity and is presumably cleaved and translocated into target cells to inhibit growth. CDI systems also encode CdiI immunity proteins, which bind and inactivate their cognate CdiA-CT toxins, thereby protecting CDI+ cells from autoinhibition. Remarkably, the CdiA-CT toxin domains are polymorphic, and accordingly their corresponding CdiI immunity proteins are also highly variable. We have identified at least 30 distinct toxin-immunity families to date. There is typically less than 20% amino acid sequence identity between different CdiA-CT/CdiI families, strongly suggesting that the protein-protein interactions underlying each CdiA-CT/CdiI complex are unique. Moreover, we have recently discovered that some CdiA-CT domains interact with specific target cell proteins termed “permissive factors”, and these binding interactions are required to activate the delivered toxins. Currently, the mechanisms by which CdiI proteins neutralize and permissive factors activate CdiA-CT toxins are not understood. We propose structural, biochemical and genetic analyses to gain insights into the intricate toxin-immunity network encoded by bacterial CDI systems. We challenge the PSI Biology Network center to assist in solving the crystal structures of at least ten distinct CdiA-CT/CdiI complexes. This proposal represents a unique opportunity to elucidate how specific binding is maintained as toxin-immunity pairs diverge through evolution.
1. Morse RP, Nikolakakis KC, Willett JL, Gerrick E, Low DA, Hayes CS, Goulding CW. Structural basis of toxicity and immunity in contact-dependent growth inhibition (CDI) systems. Proc Natl Acad Sci U S A. 2012 Dec 26;109(52):21480-5. PMCID: 3535622.
2. Aoki SK, Diner EJ, de Roodenbeke CT, Burgess BR, Poole SJ, Braaten BA, Jones AM, Webb JS, Hayes CS, Cotter PA, Low DA. A widespread family of polymorphic contact-dependent toxin delivery systems in bacteria. Nature. 2010;468(7322):439-42. PMCID: 3058911.
3. Diner EJ, Beck CM, Webb JS, Low DA, Hayes CS. Identification of a target cell permissive factor required for contact-dependent growth inhibition (CDI). Genes Dev. 2012 Mar 1;26(5):515-25. PMCID: 3305988.
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