Isolation of peritrophic membrane proteins and their secretion by Spodoptera frugiperda (Lepidoptera) larvae

R. Bolognesi 1 , A.F. Ribeiro 2 , W.R.Terra 1 & C. Ferreira 1

1 Dept. of Biochemistry, Inst. of Chemistry, Univ. of São Paulo. Av. Lineu Prestes, 748, São Paulo, 05599-970, Brazil; 2 Dept. of Biology, Univ. of São Paulo, R. do Matão, 277, São Paulo, 05508-900, Brazil

Insects have a peritrophic membrane (PM) which lines the midgut and has important roles in digestive processes and in resistance to infection by microrganisms. The PM is composed of chitin and proteins. Spodoptera frugiperda is an economically important pest, and it has type I PM, which is secreted by epithelial cells of the entire midgut. The understanding of the structure and functions of the PM may help in developing insect pest control procedures. PM proteins (peritrophins) were solubilized by treating sequentially the PM with NaCl, Chaps and urea. Two main proteins were isolated with Mr 27,000 and 33,000. Antibody raised against the Mr 33,000 protein recognized two proteins in membranes from anterior midgut microvilli and in membranes of vesicles present in the ectoperitrophic fluid. These vesicles are also associated to trypsin secretion in Spodoptera frugiperda. The antibody was used to immunocytolocalize the proteins in Spodoptera frugiperda midgut. Results showed that the peritrophins are secreted mainly by the anterior midgut and that in this part of the midgut the secretion seems to be microapocrine, with the protein present in small vesicles. In the posterior midgut, the secretion seems to be exocytic. These secretion routes are the same presented for trypsin (Jordão et al, J. Insect Physiol.45,29-37,1999), suggesting that the small vesicles present in the ectoperitrophic fluid secrete enzymes as well as PM structural proteins.

Index terms: insect midgut, peritrophins, antibody.

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