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Genes encoding proteins with peritrophin A-type chitin-binding domains in Tribolium castaneum are grouped into three distinct families based on phylogeny, expression and function

Department of Biochemistry, Kansas State University, 141 Chalmers Hall, Manhattan, KS 66506-3702, USA.
Insect biochemistry and molecular biology (Impact Factor: 3.45). 02/2010; 40(3):214-27. DOI: 10.1016/j.ibmb.2010.01.011
Source: PubMed

ABSTRACT

This study is focused on the characterization and expression of genes in the red flour beetle, Tribolium castaneum, encoding proteins that possess one or more six-cysteine-containing chitin-binding domains related to the peritrophin A domain (ChtBD2). An exhaustive bioinformatics search of the genome of T. castaneum queried with ChtBD2 sequences yielded 13 previously characterized chitin metabolic enzymes and 29 additional proteins with signal peptides as well as one to 14 ChtBD2s. Using phylogenetic analyses, these additional 29 proteins were classified into three large families. The first family includes 11 proteins closely related to the peritrophins, each containing one to 14 ChtBD2s. These are midgut-specific and are expressed only during feeding stages. We propose the name "Peritrophic Matrix Proteins" (PMP) for this family. The second family contains eight proteins encoded by seven genes (one gene codes for 2 splice variants), which are closely related to gasp/obstructor-like proteins that contain 3 ChtBD2s each. The third family has ten proteins that are of diverse sizes and sequences with only one ChtBD2 each. The genes of the second and third families are expressed in non-midgut tissues throughout all stages of development. We propose the names "Cuticular Proteins Analogous to Peritophins 3" (CPAP3) for the second family that has three ChtBD2s and "Cuticular Proteins Analogous to Peritophins 1 (CPAP1) for the third family that has 1 ChtBD2. Even though proteins of both CPAP1 and CPAP3 families have the "peritrophin A" domain, they are expressed only in cuticle-forming tissues. We determined the exon-intron organization of the genes, encoding these 29 proteins as well as the domain organization of the encoded proteins with ChtBD2s. All 29 proteins have predicted cleavable signal peptides and ChtBD2s, suggesting that they interact with chitin in extracellular locations. Comparison of ChtBD2s-containing proteins in different insect species belonging to different orders suggests that ChtBD2s are ancient protein domains whose affinity for chitin in extracellular matrices has been exploited many times for a range of biological functions. The differences in the expression profiles of PMPs and CPAPs indicate that even though they share the peritrophin A motif for chitin binding, these three families of proteins have quite distinct biological functions.

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    • "Subsequent association with cuticular proteins and the formation of an ordered network of cross-linked fibers ensues [1] [4] [5] [6] [7]. Cuticular proteins are long recognized as serving many different roles, including chemical modification of the chitin microfibrils [8], remodeling of the chitin network [9], immunological defense [10], pigmentation [11] [12] [13] [14] and cross-linking of chitin microfibrils in a process called sclerotization [15] [16]. "
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    • "The chitin-binding proteins identified are classified into four different classes based on their sequence similarity, domain organization and tissue/stage specificity of gene expression. They include chitin metabolism enzymes (chitinases and chitin deacetylases ), cuticular proteins analogous to peritrophins (CPAPs), which are proteins expressed in cuticle-forming tissues with either one (CPAP1s) or three CBDs (CPAP3s), and peritrophic matrix proteins (PMPs), which are expressed in the midgut and can contain from one to several CBDs (Jasrapuria et al., 2010; Tellam et al., 1999). 2.2. "
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