CHARACTERIZATION OF A MAJOR PERITROPHIC MEMBRANE-PROTEIN, PERITROPHIN-44, FROM THE LARVAE OF LUCILIA-CUPRINA - CDNA AND DEDUCED AMINO-ACID-SEQUENCES

The peritrophic membrane is a semi-permeable chitinous matrix lining t he gut of most insects and is thought to have important roles in the m aintenance of insect gut structure, facilitation of digestion, and pro tection from invasion by microrganisms and parasites, Proteins are int egral components of this matrix, although the structures and functions of these proteins have not been characterized in any detail, The peri trophic membrane from the larvae of the fly Lucilia cuprina, the prima ry agent of cutaneous myiasis in sheep, was shown to contain six major integral peritrophic membrane proteins, Two of these proteins, a 44-k Da glycoprotein (peritrophin-44) and a 48-kDa protein (peritrophin-48) together represent >70% of the total mass of the integral peritrophic membrane proteins, Peritrophin-44 was purified and its complete amino acid sequence was determined by cloning and sequencing the DNA comple mentary to its mRNA The deduced amino acid sequence codes for a protei n of 356 amino acids containing an amino-terminal signal sequence foll owed by five similar but nonidentical domains, each of approximately 7 0 amino acids and characterized by a specific register of 6 cysteines, One of these domains was also present in the noncatalytic regions of chitinases from Brugia malayi, Manduca sexta, and Chelonus, Peritrophi n-44 has a uniform distribution throughout the larval peritrophic memb rane. Reverse transcriptase-polymerase chain reaction detected the exp ression of peritrophin-44 in all three larval instars but only trace l evels in adult L. cuprina, The protein binds specifically to tri-N-ace tyl chitotriose and reacetylated chitosan in vitro, It is concluded th at the multiple cysteine-rich domains in peritrophin-44 are responsibl e for binding to chitin, the major constituent of peritrophic membrane , Peritrophin-44 probably has roles in the maintenance of peritrophic membrane structure and in the determination of the porosity of the per itrophic membrane. This report represents the first characterization o f an insect peritrophic membrane protein.