A Novel Family of Chitin-binding Proteins from Insect Type 2 Peritrophic Matrix
cDNA SEQUENCES, CHITIN BINDING ACTIVITY, AND CELLULAR
LOCALIZATION*
Gene
Wijffels
§,
Craig
Eisemann,
George
Riding,
Roger
Pearson,
Alun
Jones¶,
Peter
Willadsen, and
Ross
Tellam
From the Commonwealth Scientific and Industrial
Research Organization Livestock Industries, Molecular Animal
Genetics Centre and the ¶ Institute of Molecular Biosciences,
Level 8, Gehrmann Laboratories, The University of Queensland,
St. Lucia, Queensland, 4072, Australia
The peritrophic matrix is a prominent feature of
the digestive tract of most insects, but its function, formation, and
even its composition remain contentious. This matrix is a molecular sieve whose toughness and elasticity are generated by glycoproteins, proteoglycans, and chitin fibrils. We now describe a small, highly conserved protein, peritrophin-15, which is an abundant component of
the larval peritrophic matrices of the Old World screwworm fly,
Chrysomya bezziana, and sheep blowfly, Lucilia
cuprina. Their deduced amino acid sequences code for a 8-kDa
secreted protein characterized by a highly conserved and novel register
of six cysteines. Two Drosophila homologues have also been
identified from unannotated genomic sequences. Recombinant
peritrophin-15 binds strongly and specifically to chitin; however, the
stoichiometry of binding is low (1:10,000 N-acetyl
glucosamine). We propose that peritrophin-15 caps the ends of the
chitin polymer. Immunogold studies localized peritrophin-15 to the
peritrophic matrix and specific vesicles in cells of the cardia, the
small organ of the foregut responsible for peritrophic matrix
synthesis. The vesicular contents are disgorged at the base of
microvilli underlying the newly formed peritrophic matrix. This is the
first time that the process of synthesis and integration of a
peritrophic matrix protein into the nascent peritrophic matrix has been observed.
*
This research was funded in part by the Australian Center
for International Agricultural Research and the L. W. Bett Trust.The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EMBL Data Bank with accession number(s) AF327453 and AF327454.
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