ATTACIN - AN INSECT IMMUNE PROTEIN - BINDS LPS AND TRIGGERS THE SPECIFIC-INHIBITION OF BACTERIAL OUTER-MEMBRANE PROTEIN-SYNTHESIS

Attacin is a 20 kDa antibacterial protein, originally isolated from th e immune haemolymph of Hyalophora cecropia, It has been demonstrated p reviously that attacin causes increased permeability of the outer memb rane of Escherichia coli and inhibition of outer-membrane protein synt hesis at the transcriptional level. This is accompanied by inhibition of growth, Here, LPS is shown to serve as the receptor for attacin and evidence is presented that attacin does not need to enter the cell to exert its activity. The increase in outer-membrane permeability prece des any increase in inner-membrane permeability by at least one genera tion time (similar to 45 min), and the inhibiting effect of attacin on synthesis of outer-membrane proteins is detectable after only 10 min. It is also shown that attacin causes induction of several stress prot eins and increased synthesis of LPS within, respectively, 25 and 60 mi n of treatment. Based on the results presented, it is proposed that at tacin has the unique ability to specifically interfere with synthesis of outer-membrane proteins without entering the inner membrane or cyto plasm.