Unraveling the essential role of CysK in CDI toxin activation

• DOI: 10.1073/pnas.1607112113
• Publication Date: 2016-08-17T02:00:34Z
• Authors: Parker M. Johnson; Christina M. Beck; Robert P. Morse; Fernando Garza-Sá...; David A. Low; Christopher S. Hayes; Celia W. Goulding
• Keywords: Models, Molecular; 0301 basic medicine; 570; Protein Structure; Secondary; Bacterial Toxins; Genetic Vectors; 610; Gene Expression; Crystallography, X-Ray; Protein Structure, Secondary; Substrate Specificity; tRNase activity; 03 medical and health sciences; RNA, Transfer; Models; Ruminococcus; Escherichia coli; Uropathogenic Escherichia coli; structural biology; Protein Interaction Domains and Motifs; Amino Acid Sequence; Cloning, Molecular; Cysteine Synthase; Crystallography; Binding Sites; Contact Inhibition; Protein Stability; Escherichia coli Proteins; Molecular; Biological Sciences; toxin chaperone; Recombinant Proteins; 3. Good health; Transfer; Infectious Diseases; Emerging Infectious Diseases; X-Ray; RNA; Biochemistry and Cell Biology; bacterial competition; Infection; Cloning; Protein Binding

Significance

Contact-dependent growth inhibition (CDI) systems produce toxins that inhibit competing bacteria and immunity proteins that protect against self-inhibition. The CDI toxin deployed by Escherichia coli 536 is a nuclease that only cleaves transfer RNA (tRNA) molecules when bound to the biosynthetic enzyme O -acetylserine sulfhydrylase (CysK). Here, we present crystal structures of the activated CysK/toxin binary complex and the neutralized CysK/toxin/immunity protein ternary complex. CysK significantly increases toxin thermostability and promotes its interaction with tRNA substrates. Collectively, our results indicate that CysK stabilizes the toxin fold, thereby organizing the nuclease active site for substrate recognition and catalysis. We propose that the E. coli 536 toxin may need to unfold when transferred between bacteria and that its interaction with CysK could ensure reactivation after entry into target cells.