PERMEABILITY OF BACILLUS-THURINGIENSIS CRYI TOXIN CHANNELS

During sporulation Bacillus thuringiensis produces parasporal inclusions with insecticidal activity. These parasporal inclusions consist of one or more Cry proteins. Type-I Cry proteins are active only against the larvae of lepidopteran insects. Their mode of action includes binding to specific components of the brush border membrane of larval midgut columnar cells and culminates with formation of a pore in the cell membrane. The resulting increase in cell membrane permeability leads eventually to cell lysis, disruption of gut integrity, and finally death of the insect. Recently we have been able to reconstitute both CryIA(c) toxin proteins and toxin binding proteins from the brush border membrane of insect midgut cells into planar lipid bilayers and determine the conductance of the resulting pores. The results of these determinations are compared with previous estimates of pore size obtained by less direct methods.