Domain I plays an important role in the crystallization of Cry3A in Bacillus thuringiensis

Mol Biotechnol. 2000 Oct;16(2):97-107. doi: 10.1385/MB:16:2:97.


The insecticidal bacterium Bacillus thuringiensis synthesizes endotoxin Cry proteins of two size classes, 135 and 70 kDa, and both form crystalline inclusions in cells after synthesis. Crystallization of 135-kDa proteins is due to intermolecular attraction of regions in the C-terminal half of the molecule, and the N-terminal half fails to crystallize when synthesized in vivo. Alternatively, endotoxins of the 70-kDa class such as Cry2A and Cry3A, which correspond to the N-terminal half of 135-kDa molecules, crystallize readily after synthesis. Cry molecules of this size class consist of three principal domains, but the domains responsible for crystallization are not known. To identify these domains, chimeric proteins were constructed in which Cry3A Domains I or III, or I and III were substituted for the corresponding domains in truncated Cry1C molecules. Cry1C molecules with only Cry3A Domain III did not crystallize, whereas when Cry3A Domains I and III, or Domain I alone, were substituted, large inclusions were obtained. Except for the chimera consisting of Cry3A Domains I and III and Cry1C Domain II, most chimeras were not as stable as wild-type Cry3A or truncated Cry1C. These results show that Cry3A Domain I plays an important role in its crystallization in vivo.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bacillus thuringiensis / chemistry*
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / toxicity
  • Bacterial Toxins*
  • DNA, Complementary / metabolism
  • Electrophoresis, Polyacrylamide Gel
  • Endotoxins / chemistry*
  • Endotoxins / toxicity
  • Hemolysin Proteins
  • Larva / drug effects
  • Microscopy, Electron
  • Microscopy, Phase-Contrast
  • Plasmids / metabolism
  • Polymerase Chain Reaction
  • Protein Structure, Tertiary
  • Recombinant Fusion Proteins / chemistry
  • Spodoptera / drug effects
  • Time Factors
  • Trypsin / pharmacology


  • Bacterial Proteins
  • Bacterial Toxins
  • DNA, Complementary
  • Endotoxins
  • Hemolysin Proteins
  • Recombinant Fusion Proteins
  • insecticidal crystal protein, Bacillus Thuringiensis
  • Trypsin