Objective To investigate the flexibility and mobility of the Bacillus thuringiensis toxin Cry1Aa.
Methods The graph theory-based program Constraint Network Analysis and normal mode-based program NMsim were used to analyze the global and local flexibility indices as well as the fluctuation of individual residues in detail.
Results The decrease in Cry1Aa network rigidity with the increase of temperature was evident. Two phase transition points in which the Cry1Aa structure lost rigidity during the thermal simulation were identified. Two rigid clusters were found in domains I and II. Weak spots were found in C-terminal domain III. Several flexible regions were found in all three domains;the largest residue fluctuation was present in the apical loop2 of domain II.
Conclusion Although several flexible regions could be found in all the three domains, the most flexible regions were in the apical loops of domain II.

Parasporins(PSs) represent a novel functional category of crystal proteins (Cry) produced by non-insecticidal Bacillus thuringiensisA distinct feature for PSs is their specific cytotoxicity against human cancer cells from diverse origins, other than hemolytic or insecticidal activityAs structurally/functionally Cry proteins, parasporins are expressed as protoxins that require protease cleavage for activationCurrently, identified PSs is classified into 6 groups:PS1, PS2, PS3, PS4, PS5 and PS6, which are heterogeneous in cytotoxic spectrum and activity levelSome PSs have been explored for their mode of anticancer activities, reports mainly include pore formation induced by binding to putative receptors on cell membrane and apoptosis by intracellular Ca 2+concentrationFurther work should focus on the identification of new PS or PS homologs and better understanding of their anticancer mechanism before possible application in cancer therapy.

细菌杀虫剂及其应用

第八节苏芸金杆菌的热稳定性,毒素对粘虫的影响(摘译自Wittig G 1967.Effect of heat-stalice Bacillus thuringiensis toxin on anmywaim.J Invertelr.Pathal,9(1):1～2)Maconnel&Richaidr(1959)首先报导了苏芸金杆菌所产生的一种热稳定性毒素,当把此种毒素饲以腊蛾幼虫时,对昆虫没有效应,但当注射入幼虫体内时,则可引起幼虫的死亡.以后有人分别以其他类似的热稳定性毒素作了昆虫口服实验(见Cantwell etc 1964,Burgerjon,1955).但据我们所知,以后没有关于把该毒素注射以昆虫的效果的进一步报导.