Fig. 2: Structural organization and insecticidal activity of monomeric Cry78Aa.

a Two views of the structure of Cry78Aa_13-359 (Mol A in Fig. 1a) shown as a ribbon cartoon. Monomeric Cry78Aa_13-359 has a rod-like shape, ~95 Å in length and 30 Å in diameter, comprising 21 β-sheets and 3 α-helices. All helices and sheets are indicated by numbers on the ribbons (see also Fig. s2-f). Cry78Aa_13-359 consists of an N-terminal trefoil domain (light blue) and a C-terminal β-pore-forming domain. The pore-forming domain can be further divided into the sheet domain (green), the transmembrane (TM) domain (yellow) and the sandwich domain (brown). b Cartoon representation of monomeric Cry78_155-359 (Mol B) from two perspectives. The color used for each subdomain of Cry78Aa_155-359 is identical with that in a. c Insecticidal activity of Cry78Aa against L. striatellus nymphs. The individual NTD or CTD of Cry78Aa had no detectable activity against third-instar nymphs at 25 μg ml⁻¹. Mixed NTD and CTD did not induce death of the nymphs. There was no significant difference in the death of test nymphs in these treatments compared with the buffer control. Full-length Cry78Aa killed almost all the test nymphs under the same conditions. Bars represent the mean ± SD (n = 3 independent experiments). Statistical significance was tested using One-way ANOVA, and is indicated in figures by letters (a, b, c, P < 0.05). The difference is not significant when it contains the same letters, and it is significant only when the letters are completely different. d Static light-scattering results of the full-length Cry78Aa and the pore-forming domain Cry78Aa_155-359. The black and blue lines represent the elution profiles of Cry78Aa_1-359 and Cry78Aa_155-359 in gel filtration, respectively. The calculated molecular weights (MWs) are labeled accordingly and the error represents the standard deviation of two independent experiments. The X-axis represents the elution volume of the samples, while the Y-axis on the left indicates the scales of the MW, and the Y-axis on the right indicates the UV absorbance of the samples at 280 nm. e The BBMVs of L. striatellus promoted Cry78Aa oligomer formation. Lane M: Molecular weight marker. Lane P: Pellet obtained after incubation of the Cry78Aa protein with BBMVs. Lane B: BBMVs incubated without Cry78Aa. Lane S: Supernatant obtained after incubation of Cry78Aa with BBMVs diluted 50 times. Lane C: Cry78Aa protein incubated without BBMVs, containing 60 ng of Cry78Aa protein. The immunoblots are representative of three independent experiments, the original images of immunoblots are shown in Supplementary Fig. 8.