EFFICIENT SECRETION OF ATTACIN FROM INSECT FAT-BODY CELLS REQUIRES PROPER PROCESSING OF THE PROSEQUENCE

The attacins constitute a group of immune proteins induced after bacte rial infection in the moth Hyalophora cecropia. They are synthesized a s preproproteins and undergo post-translational modification during tr ansport to the hemolymph. The processing and transport rates of attaci n were studied in its natural host as a response to infection. Monensi n totally inhibited the processing from proattacin to attacin and the radiolabeled proattacin remained intracellular. This observation indic ated that the prosequence is removed at or after the trans-Golgi compa rtment. It is also suggested that the processing of the prosequence do es not occur in acidic vesicles, as the process was not inhibited by t he weak base chloroquine. To study prosequence function, the attacin g ene and genes with mutations in the prosequence were cloned into the b aculovirus Autographa californica nuclear polyhedrosis virus. The proc essing of proattacin and the transport of attacin were studied by puls e-chase experiments with fat body isolated from Trichoplusia ni larvae . The rate of secretion from fat body was lowest for proattacin, which could not be processed to attacin, intermediate for attacins lacking the prosequence and highest for natural attacin. We could not detect a ny biological activity for proattacin.