Molecular recognition of an ADP-ribosylating Clostridium botulinum C3 exoenzyme by RalA GTPase

Kenneth P. Holbourn, J. Mark Sutton, Hazel R. Evans, Clifford Shone, K. Ravi Acharya*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Citations (Scopus)


C3 exoenzymes (members of the ADP-ribosyltranferase family) are produced by Clostridium botulinum (C3bot1 and -2), Clostridium limosum (C3lim), Bacillus cereus (C3cer), and Staphylococcus aureus (C3stau1-3). These exoenzymes lack a translocation domain but are known to specifically inactivate Rho GTPases in host target cells. Here, we report the crystal structure of C3bot1 in complex with RalA (a GTPase of the Ras subfamily) and GDP at a resolution of 2.66 Å. RalA is not ADP-ribosylated by C3 exoenzymes but inhibits ADP-ribosylation of RhoA by C3bot1, C3lim, and C3cer to different extents. The structure provides an insight into the molecular interactions between C3bot1 and RalA involving the catalytic ADP-ribosylating turn-turn (ARTT) loop from C3bot1 and helix α4 and strand β6 (which are not part of the GDP-binding pocket) from RalA. The structure also suggests a molecular explanation for the different levels of C3-exoenzyme inhibition by RalA and why RhoA does not bind C3bot1 in this manner.

Original languageEnglish
Pages (from-to)5357-5362
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number15
Publication statusPublished - 12 Apr 2005


  • ADP-ribosylation
  • Protein-protein interaction
  • X-ray crystallography


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