Structure of the mosquitocidal toxin from Bacillus sphaericus

Dirk J. Reinert, Irina Carpusca, Klaus Aktories, Georg E. Schulz*

*Corresponding author for this work

Research output: Contribution to journalArticleResearchpeer-review

20 Citations (Scopus)


The catalytic domain of a mosquitocidal toxin prolonged by a C-terminal 44 residue linker connecting to four ricin B-like domains was crystallized. Three crystal structures were established at resolutions between 2.5 Å and 3.0 Å using multi-wavelength and single-wavelength anomalous X-ray diffraction as well as molecular replacement phasing techniques. The chainfold of the toxin fragment corresponds to those of ADP-ribosylating enzymes. At pH 4.3 the fragment is associated in a C7-symmetric heptamer in agreement with an aggregate of similar size observed by size-exclusion chromatography. In two distinct crystal forms, the heptamers formed nearly spherical, D 7-symmetric tetradecamers. Another crystal form obtained at pH 6.3 contained a recurring C2-symmetric tetramer, which, however, was not stable in solution. On the basis of the common chainfold and NAD +-binding site of all ADP-ribosyl transferases, the NAD +-binding site of the toxin was assigned at a high confidence level. In all three crystal forms the NAD+ site was occupied by part of the 44 residue linker, explaining the known inhibitory effect of this polypeptide region. The structure showed that the cleavage site for toxin activation is in a highly mobile loop that is exposed in the monomer. Since it contains the inhibitory linker as a crucial part of the association contact, the observed heptamer is inactive. Moreover, the heptamer cannot be activated by proteolysis because the activation loop is at the ring center and not accessible for proteases. Therefore the heptamer, or possibly the tetradecamer, seems to represent an inactive storage form of the toxin.

Original languageEnglish
Pages (from-to)1226-1236
Number of pages11
JournalJournal of Molecular Biology
Issue number4
Publication statusPublished - 7 Apr 2006
Externally publishedYes


  • ADP-ribosyl transferases
  • NAD-binding site
  • Pierisin
  • Toxin activation and inhibition
  • X-ray crystallography


Dive into the research topics of 'Structure of the mosquitocidal toxin from Bacillus sphaericus'. Together they form a unique fingerprint.

Cite this