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Title: Domain organization and phylogenetic analysis of the chitinase family of proteins in three species of insects

Author
item ZHU, QINGSONG - KANSAS STATE UNIV
item ARAKANE, YASUYUKI - KANSAS STATE UNIV
item KRAMER, KARL - RETIRED 5430-05-30
item Beeman, Richard
item MUTHUKRISHNAN, SUBBARATNAM - KANSAS STATE UNIV

Submitted to: Insect Biochemistry and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2007
Publication Date: 3/1/2008
Citation: Zhu, Q., Arakane, Y., Kramer, K.J., Beeman, R.W., Muthukrishnan, S. 2008. Domain organization and phylogenetic analysis of the chitinase family of proteins in three species of insects. Insect Biochemistry and Molecular Biology 38: 452-466.

Interpretive Summary: Chitin is the main component of insect exoskeleton, conferring both rigidity and flexibility, and protecting the insect from injury, predation, infection, and desiccation. Chitin is also the major component of a membrane that coats the lining of the midgut, protecting it from abrasion and self-digestion. Until recently, very little has been known about the enzymes that are needed for digestion and reutilization of the old exoskeleton during the insect molting cycle. We examined the genome sequences of three insects, namely the fruit fly, the malaria mosquito, and the red flour beetle, and identified all the chitinase and chitinase-like genes in all three species. We found an unexpected level of complexity and functional specialization, and discovered the existence of five distinct classes of chitinase enzymes in each of the three insects. Evidence suggests that the various chitinases are needed in different tissues, and that some of the chitinase-like proteins have evolved new functions not directly related to chitin digestion, such as chitin binding and growth regulation. Each of these newly-discovered genes can become a target in screening assays for new biopesticides that disrupt molting and related physiological processes.

Technical Abstract: A bioinformatics investigation of three insect species with completed genome sequences has revealed that insect chitinase-like proteins (glycosylhydrolase family 18) are encoded by a rather large and diverse group of genes. We identified 15, 16, and 13 putative chitinase-like genes in the genomic databases of the red flour beetle, Tribolium castaneum, the fruit fly, Drosophila melanogaster, and the malaria mosquito, Anopheles gambiae, respectively. Chitinase-like proteins encoded by this gene family were classified into five groups based on phylogenetic analyses. Group I chitinases are the most abundant such enzymes in the molting fluid and/or integument, and represent the prototype, with a single copy each of the catalytic domain and chitin-binding domain (ChBD). Group II chitinases are unusually large-sized proteins that contain multiple catalytic domains and ChBDs. Group III chitinases contain two catalytic domains and are predicted to be membrane-anchored proteins. Group IV chitinases are the most divergent. They usually lack ChBDs and/or a serine-threonine-rich linker, and are known or predicted to be expressed in gut or fat body. Group V includes the putative chitinase-like imaginal disc growth factors (IDGFs). In each of these three insect genomes, multiple genes encode group IV and group V chitinase-like proteins. In contrast, groups I-III are each represented by a singe gene in each species.