CDNA AND DEDUCED AMINO-ACID-SEQUENCES OF A PERITROPHIC MEMBRANE GLYCOPROTEIN, PERITROPHIN-48, FROM THE LARVAE OF LUCILIA-CUPRINA

The gut of most insects is lined,vith a semi-permeable peritrophic mem brane (or peritrophic matrix) composed of chitin, proteoglycans and pr oteins. Despite the probable importance of the peritrophic membrane ir e facilitating the digestive process and protecting insects from invas ion by micro-organisms and parasites, there has been little characteri zation of the specific components and their interactions within this a cellular structure. Here we report the characterization of an integral peritrophic membrane glycoprotein, peritrophin-48, from the larvae of the fly Lucilia cuprina, a primary agent of cutaneous myiasis in shee p. Peritrophin-48 was purified from peritrophic membrane obtained by l arval culture and its location within the peritrophic: membrane determ ined by immune-fluorescence and immune-gold localizations. The cDNA co ding for peritrophin-48 was cloned and sequenced. The deduced amino ac id sequence codes for a protein of 375 amino acids containing an amino -terminal signal sequence followed by five similar, but non-identical domains, each approximately 65-70 amino acids in length and characteri sed by a specific register of six cysteines. The deduced amino acid se quence shows significant similarity to two other peritrophic membrane proteins, peritrophin-95 and peritrophin-44, from the same species. A reverse transcriptase-PCR approach indicated that there are several hi ghly related peritrophin-48 genes expressed in each individual. Revers e transcriptase-PCR also demonstrated the expression of peritrophin-48 in all three larval instars and adults but not pupae or eggs;. Peritr ophin-48 was expressed only by the cardia and by the larval midgut. A simple structural model of a basic unit of a type 2 peritrophic membra ne is presented. (C) 1998 Elsevier Science Ltd. All rights reserved.